Recent advances in tuning redox properties of electron transfer centers in metalloenzymes catalyzing the oxygen reduction reaction and H2 oxidation important for fuel cell design

Current fuel cell catalysts for the oxygen reduction reaction (ORR) and H₂ oxidation use precious metals and, for ORR, require high overpotentials. In contrast, metalloenzymes perform their respective reactions at low overpotentials using earth-abundant metals, making metalloenzymes ideal candidates for inspiring electrocatalytic design. Critical to the success of these enzymes are redox-active metal centers surrounding the active site of the enzyme. These electron transfer (ET) centers not only ensure fast ET to or away from the active site, but also tune the catalytic potential of the reaction as observed in multicopper oxidases as well as playing a role in dictating the catalytic bias of the reaction as realized in hydrogenases. This review summarizes recent advances in studying these ET centers in multicopper oxidases and heme-copper oxidases that perform ORR and in hydrogenases carrying out H₂ oxidation. Insights gained from understanding how the reduction potential of the ET centers affects reactivity at the active site in both the enzymes and their models are provided.