Following Electroenzymatic Hydrogen Production by Rotating Ring Disk Electrochemistry and Mass Spectrometry

We report on two new approaches to study H 2 -producing metalloenzymes using electrochemistry and mass spectrometry, where H + reduction is driven by hydrogenase within an electrochemically active polymer (redox polymer). Researchers have established electrochemical approaches to utilize the H 2 -processing metalloenzyme hydrogenase at electrode surfaces. However, it is more-than-often the case that hydrogenase electrodes are employed for H 2 oxidation. There is significant interest in using renewable electrical energy to drive low-potential reductive reactions such as H 2 evolution and N 2 fixation, particularly with metalloenzymes. However, much work is required to understand metalloenzymes. The use of rotating ring disk electrochemistry with hydrogenase is innovative in that it provides a live method to quantify the H 2 being produced by the enzyme. This method will be valuable in determining product distributions for such enzymes in real-time, at electrode surfaces. There is also significant interest in utilizing isotopes of enzymatic substrates when performing electrochemistry, since the rate of the reaction corresponds to the current at the electrode. However, researchers of electroenzymatic H + reduction have yet to utilize online mass spectrometry to analyze the products of hydron reduction. We report on the ability to follow and differentiate the formation of H 2 , HD and D 2 in real-time, permitting the calculation of apparent kinetic isotope effects. This approach will be valuable to characterizing rate-limiting steps involving H + , as well as for other gas-processing metalloenzymes.