Direct and indirect light energy harvesting with films of ambiently deposited ZnO nanoparticles

Indirect photoelectrochemical processes are possible when employing a palladium film to separate photochemical and electrochemical reactions. Here, an exploratory indirect photoelectrochemical system is developed based on ZnO or Pt@ZnO nanoparticle photocatalysts ambiently deposited onto platinum, glassy carbon, or palladium membrane electrodes and exposed to blue (385 nm) LED light in the presence of glucose hole quencher (in aqueous NaCl). It is demonstrated that under these conditions photo-excitation followed by charge transport of conduction band electrons via inter-grain conduction across ZnO particles triggers the photo-current responses. The conduction band electrons then trigger formation of interstitial hydrogen in a palladium membrane. Transport of the hydrogen across the palladium membrane into the electrochemical compartment occurs within 1–2 min of switching on the light. A proof-of-principle fuel cell with oxygen gas diffusion electrode (cathode) and indirect photo-anode is shown to operate with up to 28 μW cm−2 power output during illumination. Important power-limiting parameters and suggestions for future improvements are discussed.