The most efficient catalysts for solar fuel production should operate close to reversible
potentials, yet possess a bias for the fuel-forming direction. Protein film electrochemical
studies of Ni-containing carbon monoxide dehydrogenase and [NiFeSe]-hydrogenase, each
a reversible electrocatalyst, show that the electronic state of the electrode strongly biases the
direction of electrocatalysis of CO2/CO and H+/H2 interconversions. Attached to graphite
electrodes, these enzymes show high activities for both oxidation and reduction, but there is …

Cadmium acetate, thiourea and ammonia solution (28-30%) for the synthesis of CdS thin
film electrodes were obtained from Sigma-Aldrich. For the preparation of TiO2 thin film
electrodes, nitric acid was purchased from Fisher Scientific, and the TiO2 particles were
Degussa P25 (80% anatase, 20% rutile, average diameter 21 nm). Indium tin oxide (ITO)-
coated glass slides, used as substrates on which to grow semiconductor thin films, were
purchased from SPI, USA.