p-n junction induced space-charged localization of single-atom catalysts for boosting oxygen reduction reaction

p-n junction induced space-charged localization of single-atom catalysts for boosting oxygen reduction reaction | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article p-n junction induced space-charged localization of single-atom catalysts for boosting oxygen reduction reaction Guanjie He, Zheng Li, Qiyou Wang, Mengran Wang, Hao Cheng, Yao Lu, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4513180/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The M-N x single-atom catalysts (SACs) are critical for efficient energy conversion technologies. However, most SACs with M-N x moiety (M: Fe, Co, or/and Mn) suffer the strong binding ability with OH* intermediates in oxygen reduction reaction (ORR), which becomes a bottleneck in accelerating the kinetics. Herein, a universal “space-charged localization effect” strategy is proposed by constructing a p- n junction, where an n -type ZnS semiconductor longitudinally bridges with p -type M-N x moiety to weaken the interaction of M-Nx with OH*. As expected, the a -ZnS/Fe-NSC electrocatalyst exhibits remarkable intrinsic activity in alkaline media with a half-wave potential of 0.90 V vs. RHE, and long-term durability (a shift of only 10 mV in E 1/2 after 8,000 cycles). This phenomenon can be ascribed to the optimization of electronic structure, the S-MN 4 site can effectively activate the M center with the intermediate spin state which possesses one eg electron (t 2g 4 e g 1) readily penetrating the antibonding π-orbital of oxygen. Moreover, it offers a superior power density and higher discharge voltage in Al-air batteries. This universal strategy provides a rational perspective for the design of SACs and electronic structure engineering to construct robust active sites for high-performance oxygen reduction. Physical sciences/Chemistry/Catalysis/Electrocatalysis Physical sciences/Energy science and technology/Fuel cells Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Main Text The oxygen reduction reaction (ORR) plays an indispensable role in next-generation electrochemical energy storage devices such as metal-air batteries and fuel cells 1 – 3 . However, the sluggish ORR kinetics occurring on the cathode involve multiple reaction intermediates, and the overall efficiency is severely limited 4 – 6 . It is widely known that single-atom catalysts (SACs) with M-N x moiety (M: Fe, Co, or/and Mn) show promising ORR performance due to explicit active sites and maximum atom-utilization efficiency 7 , 8 . Previously, several reports indicate that most M-N x moieties exhibit p -type semiconductor properties due to mobile π-electron and localized d -electron interactions 9 , in which a preponderance during ORR processes would endow a potential activity 10 , 11 . However, the strong M m+ /OH * interactions and stable M (m+1)+ -O 2 2− bonds of the metal atom with a square-planar D 4h symmetry structure directly lead to slow reaction kinetics and require high overpotentials to drive the reaction 12 . This phenomenon impedes the widespread application of SACs for ORR. Compared to increasing the density of the M-N x moiety, modulating the electronic ground state of the metal centers would be an effective avenue to stimulate the intrinsic activity of SACs. Many strategies have been proposed to tune the electronic ground states of single metal centers, including forming axial coordination 13 , 14 , heteroatom tethering 15 , and low-coordination 16 , etc. While tremendous progress has been made in developing SACs with regulated local coordination environments, complex ORR processes are prone to the loss of the organic ligands, leading to unstable electronic structures of the metal center. To address these bottlenecks, n -type semiconductors as favorable supports for SACs, such as ZnS, CdS, GaS, etc., have attracted great attention to obtaining a stable structure 17 – 19 . The n -type semiconductors with a large differential work function are chosen as the support for the p -type M-N x moiety, facilitating the transfer of electrons from the electron-rich n -type semiconductors to the p -type M-N x moiety with electron holes. As the positive and negative charges cross the interface and redistribute, the electric field formed can effectively tune the electronic structure of M-N x and achieve enhanced SACs activities. Among different semiconductors, ZnS has proved to be one of the most promising n -type semiconductors due to its high work function (WF) and broad band gap. Furthermore, the high WF of ZnS modulates the low WF of M-N x to achieve a neutral WF, thus achieving a perfect pairing of strong and weak adsorption. However, systematic explorations on stimulating the ORR activity via modifying the electronic ground state of the active metal centers around SACs are rare. Here, we proposed a universal strategy, so named “space-charged localization effect” to enhance the intrinsic activity of SACs, where an n -type ZnS semiconductor is introduced into p -type M-N x sites to weaken its binding with OH*. The ZnS selected in this study promotes the formation of space-charged regions because of its high WF and suitable electronegativity. We demonstrate that the drastic thermal reduction involving Zn precursors is a simple, versatile, and scalable method for constructing unique longitudinally bridged structures. Extensive theoretical analyses reveal that p - n junction appears at the interface to form space-charged localization, forwarding the Fe 3+ spin state from low spin (t 2g 5 e g 0) to intermediate spin (t 2g 4 e g 1), readily penetrating the antibonding π-orbital of oxygen, and thus allowing an excellent ORR performance in alkaline media. It is believed that this universal route is valid to other electrocatalysts that feature strong binding interactions with OH* and thus creates possibilities to design low-cost and long-term ORR electrocatalysts for energy conversion, even at an industrial scale. Results Theoretical calculations. M-N x moiety behaves as p -type semiconductor characteristics due to the metal center coordinated to nitrogen donors, holes are their main carriers. ZnS behave as n -type semiconductor characteristics due to a wide band gap (1.96 eV), electrons are their main carriers. Under non-contact conditions, significant differences can be found between the Fermi energy levels (E f ) of SACs and ZnS (Fig. 1 a). After intimate contact, holes on the M-N x moiety will diffuse to the ZnS side, meanwhile, electrons perform motion from the M-N x site to the ZnS side. As carriers cross the interface and recombine, opposite space-charged regions form at the p - n junction, which results in energy level shifting and band edge bending. ZnS has a strong capacity to obtain electrons due to the abundant electron holes in the 3 p orbital in S 20 . Accordingly, the large energy level shifts create a very strong space-charged localization region. In addition, small-sized nanomaterials are loaded on the support, and the charge transfer per atom increases, resulting in enhanced interfacial electronic interactions. As a result, p - n junctions between SACs and ZnS can accelerate electron transport and intrinsically enhance the spin state of the metal center, thereby affecting the adsorption of reaction intermediates 21 . Correspondingly, the positively charged n -type ZnS semiconductor facilitates the adsorption of O 2 , while the negatively charged SACs accelerate the conversion of OH* and boost the ORR 22 . Further density functional theory (DFT) calculations verified the design concept. a -ZnS/Fe-NSC (ZnS anchored FeN 4 materials on the N/S-doped carbon) shows an axially asymmetric distribution of electrons at the S-FeN 4 moiety, with strong electron localization at the axial S atom (Fig. 1 b-c and Supplementary Fig. 1–2). On the contrary, Fe-NSC (N/S-doped carbon that anchors atomically dispersed FeN 4 material) presents a symmetric charge distribution. By analyzing the charge density, the charge density of in-plane FeN 4 moiety has minor change due to their weak interaction. The alteration of the DOS in a -ZnS/Fe-NSC indicates electron transfer from Fe to S (Supplementary Fig. 3). It is proved that the charged active center generated in the p - n junction facilitates the electron transfer from the n -type semiconductor ZnS to the p -type M-N x moiety. Therefore, the p - n junction between ZnS and FeN 4 induced space-charged localization at the ZnS/Fe-NSC interface, which favors the activation of O-O fracture. The rate-determining step of ORR was considered to be related to the desorption of OH* for the FeN 4 site. The orbital interactions between the Fe center and adsorbed OH* were further analyzed. According to the PDOS results in Fig. 1 d-e and Supplementary Fig. 4, compared with Fe-NSC, the 3 d electrons of Fe and 2p electrons of O in a -ZnS/Fe-NSC form a stronger hybrid state below the Fermi level. The 3 d orbitals of Fe in a -ZnS/Fe-NSC are less localized compared to Fe-NSC, especially for 3 d xz , 3 d yz , and 3 d z2 orbitals. The 3 d z2 , 3 d xz , and 3 d yz orbitals of the Fe center of a -ZnS/Fe-NSC partially overlap with the 2 p -orbitals of O near the Fermi level, indicating that Fe-O has both π-bonds and σ-bonds, which enhance the spin polarization of oxygen. The PDOSs of Fe d z2 and OH* σ (Fe d xz /d yz and OH* 2π*) overlap significantly, and this strong interaction is sufficient to split into bonding and antibonding orbitals. Meanwhile, the d band center of a -ZnS/Fe-NSC (-1.89 eV) is significantly lower than that of Fe-NSC (-0.67 eV), which leads to reduced energy levels of bonding and antibonding states of both d z2 -σ and d xz /d yz -π* in a -ZnS/Fe-NSC, accelerating the oxygen reaction. Subsequently, combined with d band center theory, the first electron-affinity (Fig. 1 f) of a -ZnS/Fe-NSC and Fe-NSC with Fe center ligands was assessed by isolated electrons (E iso−ele ). The adsorption and desorption behavior of surface intermediates at the active site is directly related to the electronic structure of the catalyst 23 , 24 . The increase of the first-electron-affinity of the ligand on the Fe center will increase the E iso−ele and OH* conversion capacity will be further enhanced. Compared to Fe-NSC (-3.1 eV), a -ZnS/Fe-NSC has a higher E iso−ele (-2.0 eV), i.e., a -ZnS/Fe-NSC, which has SACs in p - n junctions to drive stronger adsorption of O 2 *, and therefore OH* is more likely to desorb and produce OH − . In addition, the free energy diagrams for ORR processes of Fe-NSC, a -ZnS/Fe-NSC, and ZnS were investigated as shown in Fig. 1 g and Supplementary Fig. 5. The a -ZnS/Fe-NSC, Fe-NSC, and ZnS models at a potential of U = 0 V show a downhill trend for all reaction steps, indicating that the reaction proceeds spontaneously. At U = 0.46 V, the free energy of the rate-determining step (*OH) for ORR on a -ZnS/Fe-NSC, Fe-NSC, and ZnS are 0.01, 0.55, and 1.23 eV, demonstrating that the desorption process of *OH from the active site in a -ZnS/Fe-NC is kinetically more favourable (Supplementary Table 1–2). The binding of *OH is so strong that the desorption of *OH becomes the rate-determining step (RDS) of the entire reaction process, leading to the blocking of subsequent processes. Therefore, decreasing the binding energy strength of *OH can facilitate the kinetics of ORR effectively. These results demonstrate that the space-charged localization effect indeed accelerates the ORR process. a -ZnS/Fe-NSC catalysts synthesis and characterization. As shown in Fig. 2 a, the interaction of Zn with S-containing groups was induced by adding more reactive Zn to the precursors that are self-assembled from L-cysteine, melamine, and FeCl 3 powder. Melamine was thermally polymerized in the first stage (550°C) to produce g-C 3 N 4 , which provided a soft template for L-cysteine 24 . With the further increase of carbonization temperature, ZnS anchored FeN 4 materials on the N/S-doped carbon was formed ( a -ZnS/Fe-NSC). Without the addition of Zn, N/S-doped carbon that anchors atomically dispersed FeN 4 material was formed (Fe-NSC). Intriguingly, a carbon skeleton loaded with supremely active and highly utilized axial S-FeN 4 active sites was obtained. The metal element contents in a -ZnS/Fe-NSC (Fe: 1.89 wt %, Zn: 2.44 wt %) and Fe-NSC (Fe: 1.53 wt %) electrocatalysts were obtained by inductively coupled plasma optical emission spectrometer analysis. The chemical composition and crystal structure of the electrocatalysts were first characterized by X-ray diffraction patterns (XRD). It is noted that the characteristic peak that appeared at 26.4° is assigned to the (002) planes of a -ZnS/Fe-NSC and Fe-NSC are broader, indicating a large number of graphene sheets in both two samples (Supplementary Fig. 6). Other characteristic diffraction peaks of the a -ZnS/Fe-NSC electrocatalysts correspond to the hexagonal ZnS (PDF#36-1450). As described by Raman spectroscopy, the intensity ratio of the D-band to the G-band ( I D / I G ) of the a -ZnS/Fe-NSC (0.98) is higher than that of Fe-NSC (0.95), indicating Zn-assisted thermal treatment produced defects (Supplementary Fig. 7) 25 , 26 . The electron paramagnetic resonance (EPR) results also supported this result (Supplementary Fig. 8) 27 , 28 . Transmission electron microscopy (TEM) images show ZnS loaded on carbon nanosheets (Fig. 2 b). Figure 2 c illustrates the lattice fringe spacing of 0.318 nm which corresponds to the (002) plane of hexagonal ZnS. The elemental mapping images demonstrate C, N, S, Zn, and Fe elements overlap on a -ZnS/Fe-NSC surface (Fig. 2 e). The aberration-corrected high-angle annular dark-field scanning TEM (AC-HAADF-STEM) was performed to made the evidence of atomic Fe. The Fe atoms are uniformly dispersed on the ZnS particle support (Fig. 2 d). In contrast, the morphology of Fe-NSC nanosheets is nonuniform, multilayer folded structure with disordered lattice stripes, consisting of amorphous carbon (Supplementary Fig. 9). Meanwhile, there is no obvious iron particle agglomeration on the surface of Fe-NSC nanosheets. Investigating the electronic structures. To investigate the electron states and coordination environments of the metal centers, high-resolution X-ray photoelectron spectroscopy (XPS) and simultaneous X-ray absorption near edge spectroscopy (XANES) were performed (Fig. 3 a-e). The Fe 2p XPS spectra for a -ZnS/Fe-NSC and Fe-NSC show that the Fe species exist as the Fe-N, Fe 2+ , and Fe 3 + 29 . The peaks of Fe species in a -ZnS/Fe-NSC are negatively shifted by 0.5 eV relative to that of Fe-NSC, indicating more negative oxidation states. A similar phenomenon has been observed in S-doped SACs electrocatalysts, which may be caused by the neighboring S atoms 30 . The deconvolution of XPS S 2p spectra determines Zn-S (32%, 161.7 eV), C-S-C (28%, 163.6 eV), Fe-S (19%, 165.8 eV), and S-O (21%, 168.6 eV) species for a -ZnS/Fe-NSC (Supplementary Table 3) 31 , 32 . It is worth noting that Fe-NSC is dominated by the C-S bond, and there is no Zn-S and Fe-S bond in Fe-NSC. Furthermore, there is a significant increase in the fitted ratio of Fe-S to Fe-N bonds in a-ZnS/Fe-NSC compared to Fe-NSC, suggesting that more axial S in a -ZnS/Fe-NSC are coordinated to the FeN 4 site. The contents of the C/N conformations in ZnS/Fe-NSC and Fe-NSC electrocatalysts are significantly different (Supplementary Fig. 10 and Table 4–6) 33 and a -ZnS/Fe-NSC possesses abundant Fe-N and C = C bonds 34 . These changes in bond energy led to changes in electronic structures attributed to the formation of p - n junctions. FeN 4 behaves as p -type semiconductor characteristics that tend to act as electron acceptors, resulting in a negative shift in bond energy. ZnS as an n -type semiconductor exhibits a positive shift in bond energy owing to its partial positive charge. The electrons in ZnS are gradually transferred to FeN 4 as the p - n junction is formed, resulting in a downward shift of the d -band center, which is consistent with the results of DFT. Correspondingly, the adsorption/dissociation behavior of oxygen-containing intermediates on the a -ZnS/Fe-NSC catalyst surface is optimized, accelerating ORR processes. Fe K-edge XANES spectrum shows a positive shift in a -ZnS/Fe-NSC compared to Fe-NSC, indicating the electronic structure change of Fe. XANES fitting results show that the average Fe oxidation state in a -ZnS/Fe-NSC (+ 2.8) is higher than that of Fe-NSC (+ 2.2) 35 . It should be mentioned that a -ZnS/Fe-NSC exhibits a different shoulder peak (7113.7 eV) to FePc with in-plane FeN 4 structure (7110.8 eV), which can be attributed to the axial Fe-S bond breaking square-planar configuration with D 4h symmetry 36 , 37 . The introduction of the p - n junction breaks the symmetry of the local FeN 4 structure. Compared to FePc and Fe-NSC, the introduction of ZnS results in a significant change in the shape of the spectra, indicating the presence of new coordination modes, such as Fe-S, where not only is the primary peak suppressed and broadened, but also the second peak from the Fe-N/C path disappears. Moreover, the least-square EXAFS curve fitting analysis method was used to obtain structural insights into a -ZnS/Fe-NSC. In a -ZnS/Fe-NSC, the bond length of Fe-N is reduced as expected and its coordination number of 4.7 is much higher than that of Fe-NSC (3.9), indicating that the path amplitude of Fe-N is optimized (Supplementary Table 7). These changes experimentally verify the molecular distortion caused by the extension of the Fe-N bond and the presence of additional Fe-S. Interestingly, the k 3 weighting increases the shell amplitude relative to the k 2 weighting, again reflecting the contribution of Fe-S scattering. In the wavelet transform (WT) analysis (Supplementary Fig. S11), the maximum value of a -ZnS/Fe-NSC is similar to FePc, but slightly shifted towards FeS 2 indicating the presence of Fe-S bonds in a -ZnS/Fe-NSC. The doublet peaks (D1 and D5) in the 57 Fe Mössbauer spectrum of FeN 4 , as depicted in Fig. 3 f, are indicative of the square planar FeN 4 species 38 . Regarding FeN 4 -S, two distinct D2 and D4 doublet peaks are visible along with a small D1 doublet peak. Notably, the D3 peaks are ascribed to the S-FeN 4 sites with surface-adsorbed O 2 molecule (S-FeN 4 -O 2 ), which is absent in the spectrum of Fe-N-C 39 , 40 . These characterization results demonstrate that the active sites in a -ZnS/Fe-NSC have the FeN 4 S configuration, i.e., planar FeN 4 units with one axial S atom. To further reveal the electronic ground state of Fe, zero-field cooling (ZFC) measurements were used 41 , 42 . The curve for a -ZnS/Fe-NSC exhibits a flatter growth trend than that of Fe-NSC due to the presence of extra spins, which considers that the local moment of the Fe center increases considerably during the forming of the p - n junction. The effective magnetic moments for a -ZnS/Fe-NSC and Fe-NSC are 3.67 µB and 2.23 µB (Fig. 3 g). Meanwhile, the unpaired electron numbers (n) are obtained by the unpaired electrons equation, which is 0.96 ( a -ZnS/Fe-NSC) and 2.78 (Fe-NSC), respectively. These results prove the Fe 3+ ions of a -ZnS/Fe-NC presenting as a medium spin state, an electron is occupied in the σ* antibonding orbital, leading to a neutral interaction of Fe 3+ /O 2 43 . Certainly, the axial S coordination allows the ideal filling of Fe 3+ in FeN 4 S and presumably gives FeN 4 a much higher ORR activity (Fig. 3 h). The O 2 adsorption properties were used by O 2 temperature-programmed desorption (TPD) measurements 44 . a -ZnS/Fe-NSC exhibits a stronger O 2 adsorption response than Fe-NSC, indicating that a -ZnS/Fe-NSC has better O 2 adsorption ability than Fe-NSC (Fig. 3 i). Besides, the O 2 desorption peak located at 340°C can be attributed to the release of chemically adsorbed O 2 from the electrocatalysts 45 . The intrinsically optimized electronic ground state makes a -ZnS/Fe-NSC deliver an enhanced O 2 adsorption and activation ability. Evaluating catalyst performance for alkalinity ORR. The cyclic voltammetry (CV) was first measured to verify the ORR properties. Specifically, a -ZnS/Fe-NSC electrocatalyst exhibits a more positive onset potential ( E one , 1.17 V vs. RHE) and reduction peak (0.90 V vs. RHE), indicating an optimal ORR activity (Supplementary Fig. 12). Further half-wave potential ( E 1/2 ) was obtained via linear sweep voltammetry (LSV) curves in Fig. 4 a. a -ZnS/Fe-NSC electrocatalyst presents a high E 1/2 of 0.9 V vs. RHE, which is higher than that of Fe-NSC (0.84 V vs. RHE). To investigate the effects of temperature, Fe atom, and ZnS loading on the ORR performance of a -ZnS/Fe-NSC electrocatalysts, the loading amount of Fe atom and ZnS in such an electrocatalyst was varied during its synthesis process (Supplementary Fig. 13). LSV curves of a -ZnS/Fe-NSC-1, a -ZnS/Fe-NSC-2 (namely a -ZnS/Fe-NSC), and a -ZnS/Fe-NSC-3 electrocatalysts were also tested to explore the effect of ZnS structure on ORR performance in 0.1 M KOH (Supplementary Fig. 14–15). A reasonable ZnS size and a similar mass ratio of ZnS longitudinally bridged Fe atoms determine the ORR performance of catalysts. a -ZnS/Fe-NSC electrocatalyst presents a high kinetic current density (J k ) of 10.8 mA cm − 2 at 0.88 V (Fig. 4 b), which is more than 10 times compared to that of Fe-NSC (1.3 mA cm − 2 ). The ORR kinetics were revealed by the Tafel slope (Fig. 4 c) and Koutecky-Levich (K-L) equation (Fig. 4 d and Supplementary Fig. 16). The a -ZnS/Fe-NSC presents a low Tafel slope of 50.1 mV dec − 1 and an ideal four-electron ORR process 45 . Beyond that, the ORR performance of Fe-N-C was evaluated and compared with the a -ZnS/Fe-NSC electrocatalyst. The overpotential and Tafel slope of Fe-N-C electrocatalysts are behind of a -ZnS/Fe-NSC in 0.1 M KOH (Supplementary Fig. 17–19). The various *OH adsorption characteristics were investigated using in situ infrared (FTIR) analysis. Normally, when the applied voltage is reduced, the associative process is demonstrated by the absorption bands at 1203 and 1211 cm − 1 , which are attributed to the Fe-O stretching mode of *OH. It can be found that the *OH absorption band changes to a larger wavenumber for a -ZnS/Fe-NSC than that for FePc, suggesting a relatively weaker contact strength with the *OH, which is favorable to the detachment of ORR intermediates (Supplementary Fig. 20). Meanwhile, the performance of a -ZnS/Fe-NSC catalyst is comparable or superior to Fe-NSC electrocatalyst in 0.1M HClO 4 (Supplementary Fig. 21). As a result, the p - n junctions facilitate OH* dissociation during the ORR process. The double-layer capacitance ( C dl ) of the as-prepared electrocatalysts was measured to obtain the electrochemically active surface area (ECSA), which should be a strong parameter reflecting the intrinsic activity of the catalyst. As presented in Fig. 4 e and Supplementary Fig. 22, a -ZnS/Fe-NSC exhibits higher C dl and ESCA among all samples (115.0 mF cm − 2 / 52.5 m 2 g − 1 ) 48 . Meanwhile, the a -ZnS/Fe-NSC electrocatalyst has a site density of 1.16 × 10 19 sites per g and the criteria of turnover frequency is 0.52 e − 1 ·site − 1 ·s − 1 at 0.85 V and higher than that of Fe-NSC catalysts (8.94×10 18 sites per gram and 0.45 e − 1 ·site − 1 ·s − 1 at 0.85 V), which indicates a significant contribution of p - n junction rectification to intermediates behavior (Supplementary Fig. 23–24). Fe-NSC and a -ZnS/Fe-NSC show the nanosheet shape and the hierarchical pore structure (Supplementary Fig. 25 and Table 8). The specific surface area of Fe-NSC is slightly larger than a -ZnS/Fe-NSC, but a -ZnS/Fe-NSC presents more abundant mesoporous pores. Pore accessibility was evaluated in conjunction with ECSA of these samples. It is worth noting that the abundance of mesoporous has an important effect on the accessibility and mass transfer of active sites. To verify whether Fe-N 4 S is the main active site during the ORR, KSCN poisoning experiments were performed, since SCN − can deactivate the Fe-N 4 S site (Supplementary Fig. 26). These results demonstrated that a -ZnS/Fe-NSC p - n junction delivers outstanding ORR activity under alkaline conditions. The a -ZnS/Fe-NSC electrocatalysts present outstanding stability, which is presented by current retention of 88% after 25 h chronoamperometry and a shift of only 10 mV in E 1/2 after 8,000 cycles (Fig. 4 f). The post-characterizations were conducted to further confirm the durability of a -ZnS/Fe-NSC electrocatalyst at 0.7 V ( vs. RHE) in 0.1 M KOH, such as the XRD, TEM, and XPS analysis. The XRD patterns and TEM images of the a -ZnS/Fe-NSC electrocatalyst remain unchanged after the stability test (Supplementary Fig. 27–28). Towards the XPS spectra shown in Supplementary Fig. 29, no obvious changes of S 2p, N 1s, Zn 2p, and Fe 3d states in a -ZnS/Fe-NSC electrocatalyst are observed after running the ORR for over 20 h, suggesting its stable chemical state. The Fe and Zn ion dissolution mass were 0.0013 mg/L and 0.0033 mg/L after 15h chronoamperometry. The solubility of Fe and Zn was 1.3% and 1.5%, respectively. After 30 h chronoamperometry, the solubility of Fe and Zn was 1.5% and 1.8%, respectively. These results show that there is no significant leaching of Fe and Zn in the alkaline electrolyte under an O 2 atmosphere. Therefore, the a -ZnS/Fe-NSC electrocatalyst exhibits excellent chemical and structure stability during the long-term ORR test in 0.1 M KOH. It is attributed to robust structures of the p - n junction. To explore the practical application of a -ZnS/Fe-NSC electrocatalysts, methanol tolerance tests were experimented with at a potential of 0.7 V vs. RHE. The Pt/C electrocatalyst current immediately increases due to the oxidation reaction of Pt when injecting 3 M methanol. However, no significant current oscillation in the a -ZnS/Fe-NSC electrocatalyst (Supplementary Fig. 30) 49 . We attribute the high durability of a -ZnS/Fe-NSC not only to the chemical stability of ZnS and FeN 4 , but more importantly, to the Fe-S bonding that firmly anchors the FeN 4 sites to the ZnS surface during the ORR process. Exploring the universality of the space-charged localization effect. The designed space-charged localization effect is easily applied to other SACs with p -type semiconductor properties of the M-N x site, including Mn-NSC, Cu-NSC, and Co-NSC. XRD results of these a -ZnS/M-NSC electrocatalysts (Supplementary Fig. 31) prove their successful synthesis by the same synthesis method. The binding energy of a -ZnS/M-NSC models is smaller than that of SACs models, indicating that a -ZnS/M-NSC models have better thermodynamic stability (Fig. 5 a). The related free energy diagrams of ORR pathways on ORR processes of M-NSC (M = Cu, Co, and Mn) and a -ZnS/M-NSC (M = Cu, Co, and Mn) were investigated as shown in Supplementary Fig. S32 and Table S10-S11. the ΔG OH* value is the largest among M-NSC and a -ZnS/Fe-NSC catalysts. This indicates that the ΔG OH* are the real RDS in M-NSC and a -ZnS/Fe-NSC. ∆G *OH is an effective descriptor of the intermediate adsorption/desorption capacity, DFT calculation is performed to estimate the binding energy between OH* and a -ZnS/M-NSC and M-NSC, leading to a volcano plot in Fig. 5 b. The strong adsorption of OH* by the M-N x site tends to promote the poisoning of the M centers by adsorbate occupation and may passivate the catalyst. The incorporation of M-NSC with ZnS makes the ΔG *OH values of the M-NSC modulate to be optimized, which are 0.4, 0.8, -0.6, and 0.1 eV for the a -ZnS/Fe-NSC, a -ZnS/Co-NSC, a -ZnS/Mn-NSC, and a -ZnS/Cu-NSC model electrocatalysts, respectively. The positively charged ZnS side in the a -ZnS/M-NSC as a p - n junction would have a greater ability to transform targeted OH − (Fig. 5 c). As shown in Supplementary Fig. S33, the E f of Fe-NSC (-2.80 eV), Mn-NSC (-2.58 eV), Cu-NSC (-2.81 eV), and Co-NSC (-2.82 eV) which are lower than that of ZnS (-1.33 eV), enhancing the ORR activity of SACs. Figure 5 d shows that the J k of a -ZnS/M-NSC at 0.8V is indeed enhanced by the space-charged localization, and the OH* transformation is accelerated. These a -ZnS/M-NSC electrocatalysts also present outstanding ORR activity in 0.1 M KOH solution (Fig. 5 e), which is even better than the SACs reported in the literature (Supplementary Fig. 33 and Table 9). The E 1/2 of a -ZnS/Co-NSC, a -ZnS/Mn-NSC, and a -ZnS/Cu-NSC are 0.90, 0.90, and 0.84 V, respectively. These values are much more positive than those of the original M-NSC catalyst. The Tafel slopes of the a -ZnS/Co-NSC, a -ZnS/Mn-NSC, and a -ZnS/Cu-NSC electrocatalysts are reduced from 45.3 to 39.0 mV dec − 1 , 47.7 to 47.3 mV dec − 1 , and 50.0 to 47.9 mV dec − 1 in 0.1 M KOH solution (Fig. 5 f), respectively. From the comparative analysis of the E 1/2 of a -ZnS/M-NSC and M-NSC, the introduction of n -type ZnS with p -type MN 4 can improve the ORR performance. The aqueous Al-air batteries (AABs) were assembled to evaluate the practical performance of a -ZnS/M-NSC (Supplementary Fig. 34). The a -ZnS/M-NC cathodes all display an excellent energy density (~ 2500 Wh kg − 1 ) and a high discharge voltage (~ 1.4 V vs. Al/Al 3+ ). The performance of a -ZnS/Fe-NSC air-cathode catalyst is comparable or superior to those well-known SACs-based air-cathodes (Supplementary Table S12). The ZnS longitudinally bridge SACs induced space-charged localization effect demonstrated a versatile strategy for preparing efficient ORR electrocatalysts. Discussion In summary, a universal strategy “space-charged localization effect” by ZnS longitudinally bridging SACs ( a -ZnS/M-NSC), is proposed to accelerate OH* desorption behavior for efficient SACs catalysts. Taking a -ZnS/Fe-NSC as an instance, FeN 4 S coordination facilitates the stabilization of SACs, which is analyzed by model-dependent EXAFS fitting. The theoretical study reveals enhanced electron-affinity (E iso−ele ) on the side of SACs in p - n junctions drives stronger adsorption of O 2 * compared to Fe-NSC, and ultimately promotes oxygen reduction. ZFC, TPD, and O 2 adsorption/dissociation processes indicated an enhanced spin configuration of the Fe center (from t 2g 5 e g 0 to t 2g 4 e g 1) and accelerated OH* transfer to OH − . As a result, the a -ZnS/Fe-NSC electrocatalyst exhibits an outstanding intrinsic activity (E 1/2 =0.90 V, Tafel slope = 50.1mV dec − 1 , TOF of 0.52 e − 1 ·site − 1 ·s − 1 at 0.85 V) for alkaline ORR, which is much superior to commercial Pt/C. Displacing non-noble metal single atoms such as Mn, Co, and Cu could further lead to better ORR and AABs performances. The mechanism revealed in this work provide a reasonable idea for understanding the electrocatalytic process at the atomic level and designing efficient catalysts for energy conversion devices. Methods Materials Melamine (C 3 H 6 N 6 , AR), L-Cysteine (98%) (C₃H₇NO₂S, AR), iron chloride hexahydrate (FeCl 3 ∙6H 2 O, AR), cupric chloride (CuCl 2 ),cobalt chloride hexahydrate (CoCl 2 ·6H 2 O, AR), manganese(II) chloride tetrahydrate (MnCl 2 ∙4H 2 O), Zinc power (AR), hydrochloric acid (HCl, AR), potassium hydroxide (KOH, AR), indium hydroxide (In(OH) 3 , AR), zinc oxide (ZnO, AR), sodium stannate (Na 2 SnO 3 , AR), anhydrous ethanol (AR), Pt/C (AR) were purchased from Sigma-Aldrich and used as received without further purification. Synthesis of Fe-NSC : 6 g C 3 H 6 N 6 , 1.5 g C 3 H 7 NO 2 S and 0.12 g FeCl 3 , were mixed homogeneously and then ball milled for 8 h. Subsequently, the sample obtained above was added to 10 mL of a mixed solution of ethanol and hydrochloric acid and stirred sufficiently (The volume ratio of ethanol to hydrochloric acid is 5:1). The above slurry is stirred continuously until the solution is completely evaporated. The resulting mixture was dried under 80°C in an oven and subsequently, ball milled again for 2h. The secondary ball-milled samples were subjected to pyrolysis and carbonization in an Ar gas atmosphere, with the rate of temperature increase controlled at 3°C/min. Finally, the samples were immersed in a 2 M HCl solution to remove unstable substances. The sample obtained after the above steps is named Fe-NSC. Synthesis of a -ZnS/Fe-NSC 6 g Fe-NSC and 1.2g zinc powder mixed homogeneously and then ball milled for 2 h. Subsequently, the mixture was subjected to pyrolysis and carbonization in an Ar gas atmosphere, with the rate of temperature increase controlled at 3°C/min. The sample obtained after the above steps is named a -ZnS/Fe-NSC. Additional details regarding the materials and methods may be found in the SI Appendix. Declarations Data availability The data that support the findings of this study are available from the corresponding author upon reasonable request. Acknowledgements This work was supported by the Natural Science Foundation of China (Grants Nos. U20A20280) and UK Research and Innovation (UKRI) under the UK government's Horizon Europe funding guarantee (101077226; EP/Y008707/1). We thank the 1W1B beamline of Beijing Synchrotron Radiation Facility (BSRF) for providing beam time to support this work. Author contributions Z.L. conceived and designed the research. Z.L. and S.H. conducted the experiments and the theoretical calculations. Q.W., M.W., H.C., L.Z. and Y.L. supported the experiments and helped to analyze the results. W.Z. and J.Z. together wrote and revised the manuscript with input from all the authors. 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Mater. 35 , 2210757 (2023). Y. Wu et al. , Manipulating the electronic configuration of Fe-N 4 sites by an electron-withdrawing/donating strategy with improved oxygen electroreduction performance. Mater. Chem. Frontiers 6 , 1209-1217 (2022). Z. Zhu et al. , Coexisting single-atomic Fe and Ni sites on hierarchically ordered porous ccarbon as a highly efficient ORR electrocatalyst. Adv. Mater. 32 , e2004670 (2020). Additional Declarations There is NO Competing Interest. Supplementary Files SI.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4513180","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":314227573,"identity":"390e4ec9-6887-4f8f-880c-c51a9c8c32c4","order_by":0,"name":"Guanjie 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Electron localization functions of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC. \u003cstrong\u003ec\u003c/strong\u003e Charge density of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC. \u003cstrong\u003ed-e\u003c/strong\u003e The PDOS of Fe and O of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC and Fe-NSC catalysts. \u003cstrong\u003ef\u003c/strong\u003e E\u003csup\u003eiso-ele\u003c/sup\u003e of Fe-NSC and \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC. \u003cstrong\u003eg\u003c/strong\u003e free energy diagrams of ORR pathways on \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, Fe-NSC, and ZnS (The solid and dashed lines show the free energy variations at U = 0 V and U = 0.46 V, respectively).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4513180/v1/f26a357a7ad1400f583584dc.png"},{"id":58356814,"identity":"032cfadc-76e7-42b4-bf9f-275b1de0f10e","added_by":"auto","created_at":"2024-06-14 10:11:09","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2606729,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStructural characterization.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Schematic illustration of the synthesis of different \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalysts. \u003cstrong\u003eb\u003c/strong\u003e TEM and \u003cstrong\u003ec\u003c/strong\u003e HRTEM images of the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NC electrocatalyst. \u003cstrong\u003ed\u003c/strong\u003e AC-HAADF-STEM image of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst. \u003cstrong\u003ee\u003c/strong\u003e Elemental mapping images of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4513180/v1/c76c3af959c7b255738688e8.png"},{"id":58356811,"identity":"8ef0f9f4-8b4c-4e7e-b777-05b60fc7705c","added_by":"auto","created_at":"2024-06-14 10:11:09","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1428806,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStructural characterization.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e high-resolution XPS spectra for Fe 2p. \u003cstrong\u003eb\u003c/strong\u003e high-resolution XPS spectra for S 2p AFM image and corresponding height profile of \u003cem\u003ed\u003c/em\u003e-NiFe-LDH. \u003cstrong\u003ec \u003c/strong\u003eXANES spectra at Fe K-edge of the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, FePc, Fe foil, FeO, and Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. \u003cstrong\u003ed\u003c/strong\u003e EXAFS spectra of Fe K-edge in the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, FePc, Fe foil, FeO, and Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e.\u003cstrong\u003e e\u003c/strong\u003e FT-EXAFS fitting curves for \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC in R space. \u003cstrong\u003ef\u003c/strong\u003e \u003csup\u003e57\u003c/sup\u003eFe Mössbauer transmission spectrum of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC.\u003cstrong\u003e g \u003c/strong\u003e1/χm plots. \u003cstrong\u003eh\u003c/strong\u003e the spin-splitting of Fe 3\u003cem\u003ed\u003c/em\u003e atom orbitals for Fe-NSC and \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC after O* adsorption. \u003cstrong\u003ei\u003c/strong\u003e O\u003csub\u003e2\u003c/sub\u003e-TPD curves for \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC and Fe-NSC.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4513180/v1/80f3489554c16e8930604689.png"},{"id":58356810,"identity":"42c34450-ebb1-42a3-a00e-4196282d0456","added_by":"auto","created_at":"2024-06-14 10:11:09","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":838500,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eORR performance. a\u003c/strong\u003e LSV curves of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, Fe-NSC, and 20% Pt/C in alkaline media. \u003cstrong\u003eb\u003c/strong\u003e J\u003csub\u003ek\u003c/sub\u003e at 0.85 V vs. RHE for as-prepared catalysts. \u003cstrong\u003ec\u003c/strong\u003e Tafel slope in alkaline media. \u003cstrong\u003ed\u003c/strong\u003e LSV curves of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC at different rotating rates (inset: K-L plots). \u003cstrong\u003ee\u003c/strong\u003e ECSA normalized kinetic current densities (inset: electrochemical double-layer capacitances). \u003cstrong\u003ef\u003c/strong\u003e Normalized chronoamperometry curves of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC at the constant potential of 0.7 V vs. RHE (inset: LSV curves measured before and after 8,000 cycles at a rotation rate of 1600 rpm for 20% Pt/C, and \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4513180/v1/004b6f3851da8f7de2fadc34.png"},{"id":58357220,"identity":"661d557a-ac14-4f7c-9a51-f83bcacfde38","added_by":"auto","created_at":"2024-06-14 10:19:09","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":902087,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eReaction mechanism\u003c/strong\u003e. \u003cstrong\u003ea\u003c/strong\u003e binding energy obtained from the DFT calculations on different M-NSC and \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC model electrocatalysts. \u003cstrong\u003eb\u003c/strong\u003e a volcano plot of the ORR activity on \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC model electrocatalysts. \u003cstrong\u003ec\u003c/strong\u003e space charge localization schemes at the contacted areas of the \u003cem\u003ep\u003c/em\u003e-type MN\u003csub\u003e4\u003c/sub\u003e and n-type ZnS junction. \u003cstrong\u003ed\u003c/strong\u003e J\u003csub\u003ek\u003c/sub\u003e versus RHE, plotted as a function of the Δ\u003cem\u003eW\u003c/em\u003e between MN\u003csub\u003e4\u003c/sub\u003e and ZnS. \u003cstrong\u003ee\u003c/strong\u003e LSV curves of \u003cem\u003ea\u003c/em\u003e-ZnS/Mn-NSC, \u003cem\u003ea\u003c/em\u003e-ZnS/Co-NSC, and \u003cem\u003ea\u003c/em\u003e-ZnS/Cu-NSC in O\u003csub\u003e2\u003c/sub\u003e-saturated 0.1 M KOH solution. \u003cstrong\u003ef\u003c/strong\u003e Tafel slope of \u003cem\u003ea\u003c/em\u003e-ZnS/Mn-NSC, \u003cem\u003ea\u003c/em\u003e-ZnS/Co-NSC, and \u003cem\u003ea\u003c/em\u003e-ZnS/Cu-NSC in alkaline media.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4513180/v1/79aec079e5ea2e17062a5542.png"},{"id":61399519,"identity":"44e87bef-75ad-49a3-823f-5da2c0c177fb","added_by":"auto","created_at":"2024-07-30 09:38:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":9791311,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4513180/v1/ac9262cc-9745-4bb1-ba20-49f6b6f62748.pdf"},{"id":58356815,"identity":"b6a66296-e9f3-4a98-9327-034c1cbaa0ba","added_by":"auto","created_at":"2024-06-14 10:11:10","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":39119503,"visible":true,"origin":"","legend":"","description":"","filename":"SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-4513180/v1/a0286aacc78e0beeaba16d00.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"p-n junction induced space-charged localization of single-atom catalysts for boosting oxygen reduction reaction","fulltext":[{"header":"Main Text","content":"\u003cp\u003eThe oxygen reduction reaction (ORR) plays an indispensable role in next-generation electrochemical energy storage devices such as metal-air batteries and fuel cells\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. However, the sluggish ORR kinetics occurring on the cathode involve multiple reaction intermediates, and the overall efficiency is severely limited\u003csup\u003e\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. It is widely known that single-atom catalysts (SACs) with M-N\u003csub\u003ex\u003c/sub\u003e moiety (M: Fe, Co, or/and Mn) show promising ORR performance due to explicit active sites and maximum atom-utilization efficiency\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Previously, several reports indicate that most M-N\u003csub\u003ex\u003c/sub\u003e moieties exhibit \u003cem\u003ep\u003c/em\u003e-type semiconductor properties due to mobile π-electron and localized \u003cem\u003ed\u003c/em\u003e-electron interactions\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e, in which a preponderance during ORR processes would endow a potential activity\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. However, the strong M\u003csup\u003em+\u003c/sup\u003e/OH\u003csup\u003e*\u003c/sup\u003e interactions and stable M\u003csup\u003e(m+1)+\u003c/sup\u003e-O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e bonds of the metal atom with a square-planar D\u003csub\u003e4h\u003c/sub\u003e symmetry structure directly lead to slow reaction kinetics and require high overpotentials to drive the reaction\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. This phenomenon impedes the widespread application of SACs for ORR. Compared to increasing the density of the M-N\u003csub\u003ex\u003c/sub\u003e moiety, modulating the electronic ground state of the metal centers would be an effective avenue to stimulate the intrinsic activity of SACs.\u003c/p\u003e \u003cp\u003eMany strategies have been proposed to tune the electronic ground states of single metal centers, including forming axial coordination\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, heteroatom tethering\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, and low-coordination\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, etc. While tremendous progress has been made in developing SACs with regulated local coordination environments, complex ORR processes are prone to the loss of the organic ligands, leading to unstable electronic structures of the metal center. To address these bottlenecks, \u003cem\u003en\u003c/em\u003e-type semiconductors as favorable supports for SACs, such as ZnS, CdS, GaS, etc., have attracted great attention to obtaining a stable structure\u003csup\u003e\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. The \u003cem\u003en\u003c/em\u003e-type semiconductors with a large differential work function are chosen as the support for the \u003cem\u003ep\u003c/em\u003e-type M-N\u003csub\u003ex\u003c/sub\u003e moiety, facilitating the transfer of electrons from the electron-rich \u003cem\u003en\u003c/em\u003e-type semiconductors to the \u003cem\u003ep\u003c/em\u003e-type M-N\u003csub\u003ex\u003c/sub\u003e moiety with electron holes. As the positive and negative charges cross the interface and redistribute, the electric field formed can effectively tune the electronic structure of M-N\u003csub\u003ex\u003c/sub\u003e and achieve enhanced SACs activities. Among different semiconductors, ZnS has proved to be one of the most promising \u003cem\u003en\u003c/em\u003e-type semiconductors due to its high work function (WF) and broad band gap. Furthermore, the high WF of ZnS modulates the low WF of M-N\u003csub\u003ex\u003c/sub\u003e to achieve a neutral WF, thus achieving a perfect pairing of strong and weak adsorption. However, systematic explorations on stimulating the ORR activity \u003cem\u003evia\u003c/em\u003e modifying the electronic ground state of the active metal centers around SACs are rare.\u003c/p\u003e \u003cp\u003eHere, we proposed a universal strategy, so named \u0026ldquo;space-charged localization effect\u0026rdquo; to enhance the intrinsic activity of SACs, where an \u003cem\u003en\u003c/em\u003e-type ZnS semiconductor is introduced into \u003cem\u003ep\u003c/em\u003e-type M-N\u003csub\u003ex\u003c/sub\u003e sites to weaken its binding with OH*. The ZnS selected in this study promotes the formation of space-charged regions because of its high WF and suitable electronegativity. We demonstrate that the drastic thermal reduction involving Zn precursors is a simple, versatile, and scalable method for constructing unique longitudinally bridged structures. Extensive theoretical analyses reveal that \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junction appears at the interface to form space-charged localization, forwarding the Fe\u003csup\u003e3+\u003c/sup\u003e spin state from low spin (t\u003csub\u003e2g\u003c/sub\u003e5 e\u003csub\u003eg\u003c/sub\u003e0) to intermediate spin (t\u003csub\u003e2g\u003c/sub\u003e4 e\u003csub\u003eg\u003c/sub\u003e1), readily penetrating the antibonding π-orbital of oxygen, and thus allowing an excellent ORR performance in alkaline media. It is believed that this universal route is valid to other electrocatalysts that feature strong binding interactions with OH* and thus creates possibilities to design low-cost and long-term ORR electrocatalysts for energy conversion, even at an industrial scale.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eTheoretical calculations.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eM-N\u003csub\u003ex\u003c/sub\u003e moiety behaves as \u003cem\u003ep\u003c/em\u003e-type semiconductor characteristics due to the metal center coordinated to nitrogen donors, holes are their main carriers. ZnS behave as \u003cem\u003en\u003c/em\u003e-type semiconductor characteristics due to a wide band gap (1.96 eV), electrons are their main carriers. Under non-contact conditions, significant differences can be found between the Fermi energy levels (E\u003csub\u003ef\u003c/sub\u003e) of SACs and ZnS (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). After intimate contact, holes on the M-N\u003csub\u003ex\u003c/sub\u003e moiety will diffuse to the ZnS side, meanwhile, electrons perform motion from the M-N\u003csub\u003ex\u003c/sub\u003e site to the ZnS side. As carriers cross the interface and recombine, opposite space-charged regions form at the \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junction, which results in energy level shifting and band edge bending. ZnS has a strong capacity to obtain electrons due to the abundant electron holes in the 3\u003cem\u003ep\u003c/em\u003e orbital in S\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Accordingly, the large energy level shifts create a very strong space-charged localization region. In addition, small-sized nanomaterials are loaded on the support, and the charge transfer per atom increases, resulting in enhanced interfacial electronic interactions. As a result, \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junctions between SACs and ZnS can accelerate electron transport and intrinsically enhance the spin state of the metal center, thereby affecting the adsorption of reaction intermediates\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. Correspondingly, the positively charged \u003cem\u003en\u003c/em\u003e-type ZnS semiconductor facilitates the adsorption of O\u003csub\u003e2\u003c/sub\u003e, while the negatively charged SACs accelerate the conversion of OH* and boost the ORR\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eFurther density functional theory (DFT) calculations verified the design concept. \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC (ZnS anchored FeN\u003csub\u003e4\u003c/sub\u003e materials on the N/S-doped carbon) shows an axially asymmetric distribution of electrons at the S-FeN\u003csub\u003e4\u003c/sub\u003e moiety, with strong electron localization at the axial S atom (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb-c and Supplementary Fig.\u0026nbsp;1\u0026ndash;2). On the contrary, Fe-NSC (N/S-doped carbon that anchors atomically dispersed FeN\u003csub\u003e4\u003c/sub\u003e material) presents a symmetric charge distribution. By analyzing the charge density, the charge density of in-plane FeN\u003csub\u003e4\u003c/sub\u003e moiety has minor change due to their weak interaction. The alteration of the DOS in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC indicates electron transfer from Fe to S (Supplementary Fig.\u0026nbsp;3). It is proved that the charged active center generated in the \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junction facilitates the electron transfer from the \u003cem\u003en\u003c/em\u003e-type semiconductor ZnS to the \u003cem\u003ep\u003c/em\u003e-type M-N\u003csub\u003ex\u003c/sub\u003e moiety. Therefore, the \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junction between ZnS and FeN\u003csub\u003e4\u003c/sub\u003e induced space-charged localization at the ZnS/Fe-NSC interface, which favors the activation of O-O fracture.\u003c/p\u003e \u003cp\u003eThe rate-determining step of ORR was considered to be related to the desorption of OH* for the FeN\u003csub\u003e4\u003c/sub\u003e site. The orbital interactions between the Fe center and adsorbed OH* were further analyzed. According to the PDOS results in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed-e and Supplementary Fig.\u0026nbsp;4, compared with Fe-NSC, the 3\u003cem\u003ed\u003c/em\u003e electrons of Fe and 2p electrons of O in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC form a stronger hybrid state below the Fermi level. The 3\u003cem\u003ed\u003c/em\u003e orbitals of Fe in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC are less localized compared to Fe-NSC, especially for 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003exz\u003c/em\u003e\u003c/sub\u003e, 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003eyz\u003c/em\u003e\u003c/sub\u003e, and 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003ez2\u003c/em\u003e\u003c/sub\u003e orbitals. The 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003ez2\u003c/em\u003e\u003c/sub\u003e, 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003exz\u003c/em\u003e\u003c/sub\u003e, and 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003eyz\u003c/em\u003e\u003c/sub\u003e orbitals of the Fe center of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC partially overlap with the 2\u003cem\u003ep\u003c/em\u003e-orbitals of O near the Fermi level, indicating that Fe-O has both π-bonds and σ-bonds, which enhance the spin polarization of oxygen. The PDOSs of Fe \u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003ez2\u003c/em\u003e\u003c/sub\u003e and OH* σ (Fe \u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003exz\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/d\u003c/em\u003e\u003csub\u003e\u003cem\u003eyz\u003c/em\u003e\u003c/sub\u003e and OH* 2π*) overlap significantly, and this strong interaction is sufficient to split into bonding and antibonding orbitals.\u003c/p\u003e \u003cp\u003eMeanwhile, the \u003cem\u003ed\u003c/em\u003e band center of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC (-1.89 eV) is significantly lower than that of Fe-NSC (-0.67 eV), which leads to reduced energy levels of bonding and antibonding states of both \u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003ez2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-σ\u003c/em\u003e and \u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003exz\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/d\u003c/em\u003e\u003csub\u003e\u003cem\u003eyz\u003c/em\u003e\u003c/sub\u003e-π* in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, accelerating the oxygen reaction. Subsequently, combined with \u003cem\u003ed\u003c/em\u003e band center theory, the first electron-affinity (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef) of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC and Fe-NSC with Fe center ligands was assessed by isolated electrons (E\u003csup\u003eiso\u0026minus;ele\u003c/sup\u003e). The adsorption and desorption behavior of surface intermediates at the active site is directly related to the electronic structure of the catalyst\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. The increase of the first-electron-affinity of the ligand on the Fe center will increase the E\u003csup\u003eiso\u0026minus;ele\u003c/sup\u003e and OH* conversion capacity will be further enhanced. Compared to Fe-NSC (-3.1 eV), \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC has a higher E\u003csup\u003eiso\u0026minus;ele\u003c/sup\u003e (-2.0 eV), i.e., \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, which has SACs in \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junctions to drive stronger adsorption of O\u003csub\u003e2\u003c/sub\u003e*, and therefore OH* is more likely to desorb and produce OH\u003csup\u003e\u0026minus;\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn addition, the free energy diagrams for ORR processes of Fe-NSC, \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, and ZnS were investigated as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg and Supplementary Fig.\u0026nbsp;5. The \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, Fe-NSC, and ZnS models at a potential of U\u0026thinsp;=\u0026thinsp;0 V show a downhill trend for all reaction steps, indicating that the reaction proceeds spontaneously. At U\u0026thinsp;=\u0026thinsp;0.46 V, the free energy of the rate-determining step (*OH) for ORR on \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, Fe-NSC, and ZnS are 0.01, 0.55, and 1.23 eV, demonstrating that the desorption process of *OH from the active site in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NC is kinetically more favourable (Supplementary Table\u0026nbsp;1\u0026ndash;2). The binding of *OH is so strong that the desorption of *OH becomes the rate-determining step (RDS) of the entire reaction process, leading to the blocking of subsequent processes. Therefore, decreasing the binding energy strength of *OH can facilitate the kinetics of ORR effectively. These results demonstrate that the space-charged localization effect indeed accelerates the ORR process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003ea\u003c/b\u003e \u003cb\u003e-ZnS/Fe-NSC catalysts synthesis and characterization.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, the interaction of Zn with S-containing groups was induced by adding more reactive Zn to the precursors that are self-assembled from L-cysteine, melamine, and FeCl\u003csub\u003e3\u003c/sub\u003e powder. Melamine was thermally polymerized in the first stage (550\u0026deg;C) to produce g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e, which provided a soft template for L-cysteine\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. With the further increase of carbonization temperature, ZnS anchored FeN\u003csub\u003e4\u003c/sub\u003e materials on the N/S-doped carbon was formed (\u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC). Without the addition of Zn, N/S-doped carbon that anchors atomically dispersed FeN\u003csub\u003e4\u003c/sub\u003e material was formed (Fe-NSC). Intriguingly, a carbon skeleton loaded with supremely active and highly utilized axial S-FeN\u003csub\u003e4\u003c/sub\u003e active sites was obtained. The metal element contents in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC (Fe: 1.89 \u003cem\u003ewt\u003c/em\u003e%, Zn: 2.44 \u003cem\u003ewt\u003c/em\u003e%) and Fe-NSC (Fe: 1.53 \u003cem\u003ewt\u003c/em\u003e%) electrocatalysts were obtained by inductively coupled plasma optical emission spectrometer analysis. The chemical composition and crystal structure of the electrocatalysts were first characterized by X-ray diffraction patterns (XRD). It is noted that the characteristic peak that appeared at 26.4\u0026deg; is assigned to the (002) planes of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC and Fe-NSC are broader, indicating a large number of graphene sheets in both two samples (Supplementary Fig.\u0026nbsp;6). Other characteristic diffraction peaks of the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalysts correspond to the hexagonal ZnS (PDF#36-1450). As described by Raman spectroscopy, the intensity ratio of the D-band to the G-band (\u003cem\u003eI\u003c/em\u003e\u003csub\u003eD\u003c/sub\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e) of the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC (0.98) is higher than that of Fe-NSC (0.95), indicating Zn-assisted thermal treatment produced defects (Supplementary Fig.\u0026nbsp;7)\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. The electron paramagnetic resonance (EPR) results also supported this result (Supplementary Fig.\u0026nbsp;8) \u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTransmission electron microscopy (TEM) images show ZnS loaded on carbon nanosheets (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec illustrates the lattice fringe spacing of 0.318 nm which corresponds to the (002) plane of hexagonal ZnS. The elemental mapping images demonstrate C, N, S, Zn, and Fe elements overlap on \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC surface (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). The aberration-corrected high-angle annular dark-field scanning TEM (AC-HAADF-STEM) was performed to made the evidence of atomic Fe. The Fe atoms are uniformly dispersed on the ZnS particle support (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). In contrast, the morphology of Fe-NSC nanosheets is nonuniform, multilayer folded structure with disordered lattice stripes, consisting of amorphous carbon (Supplementary Fig.\u0026nbsp;9). Meanwhile, there is no obvious iron particle agglomeration on the surface of Fe-NSC nanosheets.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eInvestigating the electronic structures.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo investigate the electron states and coordination environments of the metal centers, high-resolution X-ray photoelectron spectroscopy (XPS) and simultaneous X-ray absorption near edge spectroscopy (XANES) were performed (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-e). The Fe 2p XPS spectra for \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC and Fe-NSC show that the Fe species exist as the Fe-N, Fe\u003csup\u003e2+\u003c/sup\u003e, and Fe\u003csup\u003e3\u0026thinsp;+\u0026thinsp;29\u003c/sup\u003e. The peaks of Fe species in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC are negatively shifted by 0.5 eV relative to that of Fe-NSC, indicating more negative oxidation states. A similar phenomenon has been observed in S-doped SACs electrocatalysts, which may be caused by the neighboring S atoms\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. The deconvolution of XPS S 2p spectra determines Zn-S (32%, 161.7 eV), C-S-C (28%, 163.6 eV), Fe-S (19%, 165.8 eV), and S-O (21%, 168.6 eV) species for \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC (Supplementary Table\u0026nbsp;3) \u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. It is worth noting that Fe-NSC is dominated by the C-S bond, and there is no Zn-S and Fe-S bond in Fe-NSC. Furthermore, there is a significant increase in the fitted ratio of Fe-S to Fe-N bonds in a-ZnS/Fe-NSC compared to Fe-NSC, suggesting that more axial S in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC are coordinated to the FeN\u003csub\u003e4\u003c/sub\u003e site. The contents of the C/N conformations in ZnS/Fe-NSC and Fe-NSC electrocatalysts are significantly different (Supplementary Fig.\u0026nbsp;10 and Table\u0026nbsp;4\u0026ndash;6)\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e and \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC possesses abundant Fe-N and C\u0026thinsp;=\u0026thinsp;C bonds\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. These changes in bond energy led to changes in electronic structures attributed to the formation of \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junctions. FeN\u003csub\u003e4\u003c/sub\u003e behaves as \u003cem\u003ep\u003c/em\u003e-type semiconductor characteristics that tend to act as electron acceptors, resulting in a negative shift in bond energy. ZnS as an \u003cem\u003en\u003c/em\u003e-type semiconductor exhibits a positive shift in bond energy owing to its partial positive charge. The electrons in ZnS are gradually transferred to FeN\u003csub\u003e4\u003c/sub\u003e as the \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junction is formed, resulting in a downward shift of the \u003cem\u003ed\u003c/em\u003e-band center, which is consistent with the results of DFT. Correspondingly, the adsorption/dissociation behavior of oxygen-containing intermediates on the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC catalyst surface is optimized, accelerating ORR processes.\u003c/p\u003e \u003cp\u003eFe K-edge XANES spectrum shows a positive shift in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC compared to Fe-NSC, indicating the electronic structure change of Fe. XANES fitting results show that the average Fe oxidation state in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC (+\u0026thinsp;2.8) is higher than that of Fe-NSC (+\u0026thinsp;2.2)\u003csup\u003e35\u003c/sup\u003e. It should be mentioned that \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC exhibits a different shoulder peak (7113.7 eV) to FePc with in-plane FeN\u003csub\u003e4\u003c/sub\u003e structure (7110.8 eV), which can be attributed to the axial Fe-S bond breaking square-planar configuration with D\u003csub\u003e4h\u003c/sub\u003e symmetry\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. The introduction of the \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junction breaks the symmetry of the local FeN\u003csub\u003e4\u003c/sub\u003e structure. Compared to FePc and Fe-NSC, the introduction of ZnS results in a significant change in the shape of the spectra, indicating the presence of new coordination modes, such as Fe-S, where not only is the primary peak suppressed and broadened, but also the second peak from the Fe-N/C path disappears. Moreover, the least-square EXAFS curve fitting analysis method was used to obtain structural insights into \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC. In \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, the bond length of Fe-N is reduced as expected and its coordination number of 4.7 is much higher than that of Fe-NSC (3.9), indicating that the path amplitude of Fe-N is optimized (Supplementary Table\u0026nbsp;7). These changes experimentally verify the molecular distortion caused by the extension of the Fe-N bond and the presence of additional Fe-S. Interestingly, the k\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e weighting increases the shell amplitude relative to the k\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e weighting, again reflecting the contribution of Fe-S scattering. In the wavelet transform (WT) analysis (Supplementary Fig. S11), the maximum value of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC is similar to FePc, but slightly shifted towards FeS\u003csub\u003e2\u003c/sub\u003e indicating the presence of Fe-S bonds in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC. The doublet peaks (D1 and D5) in the \u003csup\u003e57\u003c/sup\u003eFe M\u0026ouml;ssbauer spectrum of FeN\u003csub\u003e4\u003c/sub\u003e, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef, are indicative of the square planar FeN\u003csub\u003e4\u003c/sub\u003e species\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. Regarding FeN\u003csub\u003e4\u003c/sub\u003e-S, two distinct D2 and D4 doublet peaks are visible along with a small D1 doublet peak. Notably, the D3 peaks are ascribed to the S-FeN\u003csub\u003e4\u003c/sub\u003e sites with surface-adsorbed O\u003csub\u003e2\u003c/sub\u003e molecule (S-FeN\u003csub\u003e4\u003c/sub\u003e-O\u003csub\u003e2\u003c/sub\u003e), which is absent in the spectrum of Fe-N-C\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. These characterization results demonstrate that the active sites in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC have the FeN\u003csub\u003e4\u003c/sub\u003eS configuration, i.e., planar FeN\u003csub\u003e4\u003c/sub\u003e units with one axial S atom.\u003c/p\u003e \u003cp\u003eTo further reveal the electronic ground state of Fe, zero-field cooling (ZFC) measurements were used\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. The curve for \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC exhibits a flatter growth trend than that of Fe-NSC due to the presence of extra spins, which considers that the local moment of the Fe center increases considerably during the forming of the \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junction. The effective magnetic moments for \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC and Fe-NSC are 3.67 \u0026micro;B and 2.23 \u0026micro;B (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg). Meanwhile, the unpaired electron numbers (n) are obtained by the unpaired electrons equation, which is 0.96 (\u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC) and 2.78 (Fe-NSC), respectively. These results prove the Fe\u003csup\u003e3+\u003c/sup\u003e ions of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NC presenting as a medium spin state, an electron is occupied in the σ* antibonding orbital, leading to a neutral interaction of Fe\u003csup\u003e3+\u003c/sup\u003e/O\u003csub\u003e2\u003c/sub\u003e \u003csup\u003e43\u003c/sup\u003e. Certainly, the axial S coordination allows the ideal filling of Fe\u003csup\u003e3+\u003c/sup\u003e in FeN\u003csub\u003e4\u003c/sub\u003eS and presumably gives FeN\u003csub\u003e4\u003c/sub\u003e a much higher ORR activity (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh). The O\u003csub\u003e2\u003c/sub\u003e adsorption properties were used by O\u003csub\u003e2\u003c/sub\u003e temperature-programmed desorption (TPD) measurements\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e. \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC exhibits a stronger O\u003csub\u003e2\u003c/sub\u003e adsorption response than Fe-NSC, indicating that \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC has better O\u003csub\u003e2\u003c/sub\u003e adsorption ability than Fe-NSC (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei). Besides, the O\u003csub\u003e2\u003c/sub\u003e desorption peak located at 340\u0026deg;C can be attributed to the release of chemically adsorbed O\u003csub\u003e2\u003c/sub\u003e from the electrocatalysts\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e. The intrinsically optimized electronic ground state makes \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC deliver an enhanced O\u003csub\u003e2\u003c/sub\u003e adsorption and activation ability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eEvaluating catalyst performance for alkalinity ORR.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe cyclic voltammetry (CV) was first measured to verify the ORR properties. Specifically, \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst exhibits a more positive onset potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eone\u003c/sub\u003e, 1.17 V vs. RHE) and reduction peak (0.90 V vs. RHE), indicating an optimal ORR activity (Supplementary Fig.\u0026nbsp;12). Further half-wave potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003e1/2\u003c/em\u003e\u003c/sub\u003e) was obtained \u003cem\u003evia\u003c/em\u003e linear sweep voltammetry (LSV) curves in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst presents a high \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003e1/2\u003c/em\u003e\u003c/sub\u003e of 0.9 V vs. RHE, which is higher than that of Fe-NSC (0.84 V vs. RHE). To investigate the effects of temperature, Fe atom, and ZnS loading on the ORR performance of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalysts, the loading amount of Fe atom and ZnS in such an electrocatalyst was varied during its synthesis process (Supplementary Fig.\u0026nbsp;13). LSV curves of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC-1, \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC-2 (namely \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC), and \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC-3 electrocatalysts were also tested to explore the effect of ZnS structure on ORR performance in 0.1 M KOH (Supplementary Fig.\u0026nbsp;14\u0026ndash;15). A reasonable ZnS size and a similar mass ratio of ZnS longitudinally bridged Fe atoms determine the ORR performance of catalysts.\u003c/p\u003e \u003cp\u003e \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst presents a high kinetic current density (J\u003csub\u003ek\u003c/sub\u003e) of 10.8 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at 0.88 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb), which is more than 10 times compared to that of Fe-NSC (1.3 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e). The ORR kinetics were revealed by the Tafel slope (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec) and Koutecky-Levich (K-L) equation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed and Supplementary Fig.\u0026nbsp;16). The \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC presents a low Tafel slope of 50.1 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and an ideal four-electron ORR process\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e. Beyond that, the ORR performance of Fe-N-C was evaluated and compared with the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst. The overpotential and Tafel slope of Fe-N-C electrocatalysts are behind of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC in 0.1 M KOH (Supplementary Fig.\u0026nbsp;17\u0026ndash;19). The various *OH adsorption characteristics were investigated using in situ infrared (FTIR) analysis. Normally, when the applied voltage is reduced, the associative process is demonstrated by the absorption bands at 1203 and 1211 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which are attributed to the Fe-O stretching mode of *OH. It can be found that the *OH absorption band changes to a larger wavenumber for \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC than that for FePc, suggesting a relatively weaker contact strength with the *OH, which is favorable to the detachment of ORR intermediates (Supplementary Fig.\u0026nbsp;20). Meanwhile, the performance of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC catalyst is comparable or superior to Fe-NSC electrocatalyst in 0.1M HClO\u003csub\u003e4\u003c/sub\u003e (Supplementary Fig.\u0026nbsp;21). As a result, the \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junctions facilitate OH* dissociation during the ORR process.\u003c/p\u003e \u003cp\u003eThe double-layer capacitance (\u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003edl\u003c/em\u003e\u003c/sub\u003e) of the as-prepared electrocatalysts was measured to obtain the electrochemically active surface area (ECSA), which should be a strong parameter reflecting the intrinsic activity of the catalyst. As presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee and Supplementary Fig.\u0026nbsp;22, \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC exhibits higher \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003edl\u003c/em\u003e\u003c/sub\u003e and ESCA among all samples (115.0 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e / 52.5 m\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e48\u003c/sup\u003e. Meanwhile, the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst has a site density of 1.16 \u0026times; 10\u003csup\u003e19\u003c/sup\u003e sites per g and the criteria of turnover frequency is 0.52 e\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;site\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 0.85 V and higher than that of Fe-NSC catalysts (8.94\u0026times;10\u003csup\u003e18\u003c/sup\u003e sites per gram and 0.45 e\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;site\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 0.85 V), which indicates a significant contribution of \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junction rectification to intermediates behavior (Supplementary Fig.\u0026nbsp;23\u0026ndash;24). Fe-NSC and \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC show the nanosheet shape and the hierarchical pore structure (Supplementary Fig.\u0026nbsp;25 and Table\u0026nbsp;8). The specific surface area of Fe-NSC is slightly larger than \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, but \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC presents more abundant mesoporous pores. Pore accessibility was evaluated in conjunction with ECSA of these samples. It is worth noting that the abundance of mesoporous has an important effect on the accessibility and mass transfer of active sites. To verify whether Fe-N\u003csub\u003e4\u003c/sub\u003eS is the main active site during the ORR, KSCN poisoning experiments were performed, since SCN\u003csup\u003e\u0026minus;\u003c/sup\u003e can deactivate the Fe-N\u003csub\u003e4\u003c/sub\u003eS site (Supplementary Fig.\u0026nbsp;26). These results demonstrated that \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junction delivers outstanding ORR activity under alkaline conditions.\u003c/p\u003e \u003cp\u003eThe \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalysts present outstanding stability, which is presented by current retention of 88% after 25 h chronoamperometry and a shift of only 10 mV in \u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003e1/2\u003c/em\u003e\u003c/sub\u003e after 8,000 cycles (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). The post-characterizations were conducted to further confirm the durability of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst at 0.7 V (\u003cem\u003evs.\u003c/em\u003e RHE) in 0.1 M KOH, such as the XRD, TEM, and XPS analysis. The XRD patterns and TEM images of the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst remain unchanged after the stability test (Supplementary Fig.\u0026nbsp;27\u0026ndash;28). Towards the XPS spectra shown in Supplementary Fig.\u0026nbsp;29, no obvious changes of S 2p, N 1s, Zn 2p, and Fe 3d states in \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst are observed after running the ORR for over 20 h, suggesting its stable chemical state. The Fe and Zn ion dissolution mass were 0.0013 mg/L and 0.0033 mg/L after 15h chronoamperometry. The solubility of Fe and Zn was 1.3% and 1.5%, respectively. After 30 h chronoamperometry, the solubility of Fe and Zn was 1.5% and 1.8%, respectively. These results show that there is no significant leaching of Fe and Zn in the alkaline electrolyte under an O\u003csub\u003e2\u003c/sub\u003e atmosphere. Therefore, the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst exhibits excellent chemical and structure stability during the long-term ORR test in 0.1 M KOH. It is attributed to robust structures of the \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junction. To explore the practical application of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalysts, methanol tolerance tests were experimented with at a potential of 0.7 V vs. RHE. The Pt/C electrocatalyst current immediately increases due to the oxidation reaction of Pt when injecting 3 M methanol. However, no significant current oscillation in the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst (Supplementary Fig.\u0026nbsp;30)\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e. We attribute the high durability of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC not only to the chemical stability of ZnS and FeN\u003csub\u003e4\u003c/sub\u003e, but more importantly, to the Fe-S bonding that firmly anchors the FeN\u003csub\u003e4\u003c/sub\u003e sites to the ZnS surface during the ORR process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eExploring the universality of the space-charged localization effect.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe designed space-charged localization effect is easily applied to other SACs with \u003cem\u003ep\u003c/em\u003e-type semiconductor properties of the M-N\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e site, including Mn-NSC, Cu-NSC, and Co-NSC. XRD results of these \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC electrocatalysts (Supplementary Fig.\u0026nbsp;31) prove their successful synthesis by the same synthesis method. The binding energy of \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC models is smaller than that of SACs models, indicating that \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC models have better thermodynamic stability (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). The related free energy diagrams of ORR pathways on ORR processes of M-NSC (M\u0026thinsp;=\u0026thinsp;Cu, Co, and Mn) and \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC (M\u0026thinsp;=\u0026thinsp;Cu, Co, and Mn) were investigated as shown in Supplementary Fig. S32 and Table S10-S11. the ΔG\u003csub\u003eOH*\u003c/sub\u003e value is the largest among M-NSC and \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC catalysts. This indicates that the ΔG\u003csub\u003eOH*\u003c/sub\u003e are the real RDS in M-NSC and \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC. ∆G\u003csub\u003e*OH\u003c/sub\u003e is an effective descriptor of the intermediate adsorption/desorption capacity, DFT calculation is performed to estimate the binding energy between OH* and \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC and M-NSC, leading to a volcano plot in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb. The strong adsorption of OH* by the M-N\u003csub\u003ex\u003c/sub\u003e site tends to promote the poisoning of the M centers by adsorbate occupation and may passivate the catalyst. The incorporation of M-NSC with ZnS makes the ΔG\u003csub\u003e*OH\u003c/sub\u003e values of the M-NSC modulate to be optimized, which are 0.4, 0.8, -0.6, and 0.1 eV for the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC, \u003cem\u003ea\u003c/em\u003e-ZnS/Co-NSC, \u003cem\u003ea\u003c/em\u003e-ZnS/Mn-NSC, and \u003cem\u003ea\u003c/em\u003e-ZnS/Cu-NSC model electrocatalysts, respectively. The positively charged ZnS side in the \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC as a \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junction would have a greater ability to transform targeted OH\u003csup\u003e\u0026minus;\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). As shown in Supplementary Fig. S33, the E\u003csub\u003ef\u003c/sub\u003e of Fe-NSC (-2.80 eV), Mn-NSC (-2.58 eV), Cu-NSC (-2.81 eV), and Co-NSC (-2.82 eV) which are lower than that of ZnS (-1.33 eV), enhancing the ORR activity of SACs. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed shows that the J\u003csub\u003ek\u003c/sub\u003e of \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC at 0.8V is indeed enhanced by the space-charged localization, and the OH* transformation is accelerated.\u003c/p\u003e \u003cp\u003eThese \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC electrocatalysts also present outstanding ORR activity in 0.1 M KOH solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee), which is even better than the SACs reported in the literature (Supplementary Fig.\u0026nbsp;33 and Table\u0026nbsp;9). The E\u003csub\u003e1/2\u003c/sub\u003e of \u003cem\u003ea\u003c/em\u003e-ZnS/Co-NSC, \u003cem\u003ea\u003c/em\u003e-ZnS/Mn-NSC, and \u003cem\u003ea\u003c/em\u003e-ZnS/Cu-NSC are 0.90, 0.90, and 0.84 V, respectively. These values are much more positive than those of the original M-NSC catalyst. The Tafel slopes of the \u003cem\u003ea\u003c/em\u003e-ZnS/Co-NSC, \u003cem\u003ea\u003c/em\u003e-ZnS/Mn-NSC, and \u003cem\u003ea\u003c/em\u003e-ZnS/Cu-NSC electrocatalysts are reduced from 45.3 to 39.0 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 47.7 to 47.3 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 50.0 to 47.9 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in 0.1 M KOH solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef), respectively. From the comparative analysis of the E\u003csub\u003e\u003cem\u003e1/2\u003c/em\u003e\u003c/sub\u003e of \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC and M-NSC, the introduction of \u003cem\u003en\u003c/em\u003e-type ZnS with \u003cem\u003ep\u003c/em\u003e-type MN\u003csub\u003e4\u003c/sub\u003e can improve the ORR performance. The aqueous Al-air batteries (AABs) were assembled to evaluate the practical performance of \u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC (Supplementary Fig.\u0026nbsp;34). The \u003cem\u003ea\u003c/em\u003e-ZnS/M-NC cathodes all display an excellent energy density (~\u0026thinsp;2500 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and a high discharge voltage (~\u0026thinsp;1.4 V vs. Al/Al\u003csup\u003e3+\u003c/sup\u003e). The performance of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC air-cathode catalyst is comparable or superior to those well-known SACs-based air-cathodes (Supplementary Table S12). The ZnS longitudinally bridge SACs induced space-charged localization effect demonstrated a versatile strategy for preparing efficient ORR electrocatalysts.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn summary, a universal strategy \u0026ldquo;space-charged localization effect\u0026rdquo; by ZnS longitudinally bridging SACs (\u003cem\u003ea\u003c/em\u003e-ZnS/M-NSC), is proposed to accelerate OH* desorption behavior for efficient SACs catalysts. Taking \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC as an instance, FeN\u003csub\u003e4\u003c/sub\u003eS coordination facilitates the stabilization of SACs, which is analyzed by model-dependent EXAFS fitting. The theoretical study reveals enhanced electron-affinity (E\u003csup\u003eiso\u0026minus;ele\u003c/sup\u003e) on the side of SACs in \u003cem\u003ep\u003c/em\u003e-\u003cem\u003en\u003c/em\u003e junctions drives stronger adsorption of O\u003csub\u003e2\u003c/sub\u003e* compared to Fe-NSC, and ultimately promotes oxygen reduction. ZFC, TPD, and O\u003csub\u003e2\u003c/sub\u003e adsorption/dissociation processes indicated an enhanced spin configuration of the Fe center (from t\u003csub\u003e2g\u003c/sub\u003e5 e\u003csub\u003eg\u003c/sub\u003e0 to t\u003csub\u003e2g\u003c/sub\u003e4 e\u003csub\u003eg\u003c/sub\u003e1) and accelerated OH* transfer to OH\u003csup\u003e\u0026minus;\u003c/sup\u003e. As a result, the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst exhibits an outstanding intrinsic activity (E\u003csub\u003e1/2\u003c/sub\u003e=0.90 V, Tafel slope\u0026thinsp;=\u0026thinsp;50.1mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, TOF of 0.52 e\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;site\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 0.85 V) for alkaline ORR, which is much superior to commercial Pt/C. Displacing non-noble metal single atoms such as Mn, Co, and Cu could further lead to better ORR and AABs performances. The mechanism revealed in this work provide a reasonable idea for understanding the electrocatalytic process at the atomic level and designing efficient catalysts for energy conversion devices.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cstrong\u003eMaterials\u003c/strong\u003e \u003cp\u003eMelamine (C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eN\u003csub\u003e6\u003c/sub\u003e, AR), L-Cysteine (98%) (C₃H₇NO₂S, AR), iron chloride hexahydrate (FeCl\u003csub\u003e3\u003c/sub\u003e∙6H\u003csub\u003e2\u003c/sub\u003eO, AR), cupric chloride (CuCl\u003csub\u003e2\u003c/sub\u003e),cobalt chloride hexahydrate (CoCl\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO, AR), manganese(II) chloride tetrahydrate (MnCl\u003csub\u003e2\u003c/sub\u003e∙4H\u003csub\u003e2\u003c/sub\u003eO), Zinc power (AR), hydrochloric acid (HCl, AR), potassium hydroxide (KOH, AR), indium hydroxide (In(OH)\u003csub\u003e3\u003c/sub\u003e, AR), zinc oxide (ZnO, AR), sodium stannate (Na\u003csub\u003e2\u003c/sub\u003eSnO\u003csub\u003e3\u003c/sub\u003e, AR), anhydrous ethanol (AR), Pt/C (AR) were purchased from Sigma-Aldrich and used as received without further purification.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eSynthesis of Fe-NSC\u003c/b\u003e: 6 g C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eN\u003csub\u003e6\u003c/sub\u003e, 1.5 g C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eNO\u003csub\u003e2\u003c/sub\u003eS and 0.12 g FeCl\u003csub\u003e3\u003c/sub\u003e, were mixed homogeneously and then ball milled for 8 h. Subsequently, the sample obtained above was added to 10 mL of a mixed solution of ethanol and hydrochloric acid and stirred sufficiently (The volume ratio of ethanol to hydrochloric acid is 5:1). The above slurry is stirred continuously until the solution is completely evaporated. The resulting mixture was dried under 80\u0026deg;C in an oven and subsequently, ball milled again for 2h. The secondary ball-milled samples were subjected to pyrolysis and carbonization in an Ar gas atmosphere, with the rate of temperature increase controlled at 3\u0026deg;C/min. Finally, the samples were immersed in a 2 M HCl solution to remove unstable substances. The sample obtained after the above steps is named Fe-NSC.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eSynthesis of \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC\u003c/strong\u003e \u003cp\u003e6 g Fe-NSC and 1.2g zinc powder mixed homogeneously and then ball milled for 2 h. Subsequently, the mixture was subjected to pyrolysis and carbonization in an Ar gas atmosphere, with the rate of temperature increase controlled at 3\u0026deg;C/min. The sample obtained after the above steps is named \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC.\u003c/p\u003e \u003c/p\u003e \u003cp\u003eAdditional details regarding the materials and methods may be found in the SI Appendix.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Natural Science Foundation of China (Grants Nos. U20A20280) and UK Research and Innovation (UKRI) under the UK government's Horizon Europe funding guarantee (101077226; EP/Y008707/1). We thank the 1W1B beamline of Beijing Synchrotron Radiation Facility (BSRF) for providing beam time to support this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eZ.L.\u0026nbsp;conceived and designed the research.\u0026nbsp;Z.L.\u0026nbsp;and S.H. conducted the experiments\u0026nbsp;and the theoretical calculations. Q.W., M.W., H.C., L.Z. and Y.L. supported the experiments and helped to analyze the results. W.Z. and J.Z.\u0026nbsp;together wrote and revised the manuscript with input from all the authors. The project was supervised by T.Z., and G.H.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary Information\u003c/strong\u003e The online version contains supplementary material available at https://doi.org/10.1038/...\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrespondence\u003c/strong\u003e and requests for materials should be addressed to Shiwei Hu, Guanjie He, or Zhongliang Tian.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReprints and permission information\u003c/strong\u003e is available at http://www.nature.com/reprints.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eC. 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Mater. \u003c/em\u003e\u003cstrong\u003e32\u003c/strong\u003e, e2004670 (2020).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4513180/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4513180/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe M-N\u003csub\u003ex\u003c/sub\u003e single-atom catalysts (SACs) are critical for efficient energy conversion technologies. However, most SACs with M-N\u003csub\u003ex\u003c/sub\u003e moiety (M: Fe, Co, or/and Mn) suffer the strong binding ability with OH* intermediates in oxygen reduction reaction (ORR), which becomes a bottleneck in accelerating the kinetics. Herein, a universal “space-charged localization effect” strategy is proposed by constructing a p-\u003cem\u003en\u003c/em\u003e junction, where an \u003cem\u003en\u003c/em\u003e-type ZnS semiconductor longitudinally bridges with \u003cem\u003ep\u003c/em\u003e-type M-N\u003csub\u003ex\u003c/sub\u003e moiety to weaken the interaction of M-Nx with OH*. As expected, the \u003cem\u003ea\u003c/em\u003e-ZnS/Fe-NSC electrocatalyst exhibits remarkable intrinsic activity in alkaline media with a half-wave potential of 0.90 V vs. RHE, and long-term durability (a shift of only 10 mV in E\u003csub\u003e1/2\u003c/sub\u003e after 8,000 cycles). This phenomenon can be ascribed to the optimization of electronic structure, the S-MN\u003csub\u003e4\u003c/sub\u003e site can effectively activate the M center with the intermediate spin state which possesses one eg electron (t\u003csub\u003e2g\u003c/sub\u003e4 e\u003csub\u003eg\u003c/sub\u003e1) readily penetrating the antibonding π-orbital of oxygen. Moreover, it offers a superior power density and higher discharge voltage in Al-air batteries. This universal strategy provides a rational perspective for the design of SACs and electronic structure engineering to construct robust active sites for high-performance oxygen reduction.\u003c/p\u003e","manuscriptTitle":"p-n junction induced space-charged localization of single-atom catalysts for boosting oxygen reduction reaction","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-14 10:11:04","doi":"10.21203/rs.3.rs-4513180/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8a1659c6-7fef-46a4-9f96-4df78320d9b4","owner":[],"postedDate":"June 14th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":33234323,"name":"Physical sciences/Chemistry/Catalysis/Electrocatalysis"},{"id":33234324,"name":"Physical sciences/Energy science and technology/Fuel cells"}],"tags":[],"updatedAt":"2024-07-30T09:30:18+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-14 10:11:04","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4513180","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4513180","identity":"rs-4513180","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}