Hydrogen peroxide was electrochemically produced by reducing oxygen in an aqueous solution with [Co(TCPP)] as a catalyst and photovoltaic solar cell operating at 0.5 V. Hydrogen peroxide thus produced is utilized as a fuel for a one-compartment fuel cell with Ag–Pb alloy nanoparticles as the cathode.

Cobalt-containing metal oxides [perovskites (LaCoO₃, NdCoO₃, YCoO₃, La_0.7Sr_0.3CoO₃), spinel (Co₃O₄) and wolframite (CoWO₄)] have been examined as catalysts for photocatalytic water oxidation with Na₂S₂O₈ and [Ru(bpy)₃]²⁺ as an electron acceptor and a photosensitizer, respectively. Catalysts with the perovskite structure exhibited higher catalytic activity as compared with the catalysts with the spinel and wolframite structures. LaCoO₃, which stabilizes Co(III) species in the perovskite structure, exhibited the highest catalytic activity in the photocatalytic water oxidation compared with CoWO₄, Co₃O₄ and La_0.7Sr_0.3CoO₃ which contain Co(II) or Co(IV) species in the matrices. The high catalytic reactivity of LaCoO₃ possessing perovskite structure was maintained in NdCoO₃ and YCoO₃ which exclusively contain Co(III) species. Thus, the catalytic activity of Co ions can be controlled by the additional metal ions, which leads to development of highly reactive and robust catalysts for the photocatalytic water oxidation.

Photocatalytic hydrogen evolution with 2-phenyl-4-(1-naphthyl)quinolinium ion (QuPh⁺–NA) as a photocatalyst and dihydronicotinamide adenine dinucleotide (NADH) as a sacrificial electron donor has been made possible for the first time by using nickel nanoparticles (NiNPs) as a non-precious metal catalyst. The hydrogen evolution rate with the most active Ni nanoparticles (hexagonal close-packed (hcp) structure, 6.6 nm) examined here was 40% of that with commercially available Pt nanoparticles (2 nm) using the same catalyst weight. The catalytic activity of NiNPs depends not only on their sizes but also on their crystal phases. The hydrogen-evolution rate normalized by the catalyst weight increased as the size of NiNPs becomes smaller, with regard to the crystal phase, the hydrogen-evolution rate of the NiNPs with hcp structure is more than 4 times higher than the rate of the NiNPs with face-centred cubic (fcc) structure of similar size. NiNPs act as the hydrogen-evolution catalyst under the pH conditions between 4.5 and 8.0, although the hydrogen-evolution rate at pH > 7.0 was much lower as compared with the hydrogen-evolution rate at pH 4.5. A kinetic study revealed that the rate of electron transfer from photogenerated QuPh˙–NA to NiNPs was much higher than the rate of hydrogen evolution, indicating that the rate-determining step may be proton reduction or desorption of hydrogen.