Electrically conducting particle networks in polymer electrolyte as three-dimensional electrodes for hydrogenase electrocatalysis

Efficient H2 oxidation and production by hydrogenase enzymes has attracted much interest because of the possibilities it raises for clean energy cycling without the need for precious metal catalysts. Although hydrogenases are extremely active electrocatalysts, high surface-area electrode structures will be necessary if the enzymes are to find application in energy technologies. Taking inspiration from fuel cell electrode assemblies, in which metal nanoparticles are commonly mounted on particulate carbon supports encased in polymer electrolyte, we show that high surface-area hydrogenase electrodes can be constructed from enzyme-loaded pyrolytic graphite particles in pH-neutralised Nafion. Pyrolytic graphite is the favoured surface for direct electrochemistry of many redox proteins, and on sanding, yields micron-dimension platelike particles. By modifying graphite platelets with hydrogenase before assembling the particles into a network, we ensure a high, uniform enzyme coverage. Incorporation of hydrogenases into high surface-area conducting network electrodes enhanced electrocatalytic H2 oxidation currents by 30-times compared to values obtained for a planar hydrogenase electrode, while retaining efficient conductivity and H2 mass transport through the network. This approach should make it possible to directly compare enzyme and precious metal electrocatalysis and to benchmark what opportunities are possible with selective enzyme catalysts.