Nat. Commun. 9, 3675 (2018)

Enzymatic biofuel cells convert fuels, such as H2 or glucose, directly into electricity, making use of naturally derived components to drive the catalytic processes that occur at the electrodes. For example, in H2-powered biofuel cells, hydrogenase enzymes are often used at the anode to oxidize H2 to protons. Although hydrogenases are efficient catalysts for this reaction, they are typically sensitive to high potentials and to O2, limiting their stability. Now, Adrian Ruff, Wolfgang Schuhmann and colleagues in Portugal and Germany design a hydrogenase-based bioanode that is protected from these stresses using a multi-layered architecture.

The device designed by the researchers makes use of a particularly O2-sensitive hydrogenase that is embedded in a redox-active viologen-modified polymer. This polymer wires the hydrogenase to the electrode and functions as a buffer to protect against high-potential deactivation. On top of this is a second polymer layer that is not redox-active but houses two different enzymes: catalase and glucose oxidase. These enzymes work together in a cascade to protect the O2-sensitive hydrogenase by reacting glucose sacrificially with O2 and, in the process, creating anaerobic conditions. Simultaneously, via a different enzymatic cascade, glucose also acts as a reactant to generate peroxide, which is the oxidant for the system, in situ at the cathode. In chronoamperometric experiments in the presence of O2, after 6 h the H2 oxidation current of the unprotected bioanode decreases to approximately 15% of its starting value, and the protected bioanode maintains about 70% of its current over the same time period.