Oxygen evolution catalysts
In situ modify Co-Pi, Mn-MePi and Ni-Bi with other metals eg Ni, Fe, Cr, Mo, and Zn.
In 2008, Kanan et al. reported the in situ formation of oxygen-evolution catalyst Co-Pi in neutral buffer solution.1 After that, it has attracted much interest because of its efficiency at neutral pH, electrochemical self-assembly from earth-abundant materials, and for its self-repair mechanism. We are modifying Co-Pi with Cr, Mo, Fe, Ni during in situ formation. We found that adding Cr ions during electrodeposition can improve the catalytic of Co-Pi 15% performance. The possible reason is morphology modification.
Metal(s) hydroxides or layered double hydroxides
Through electrodeposition, we prepared a series of metal hydroxides and layered hydroxide which showed promising catalytic in our group and by other groups. 2 These metal hydroxides include NiFeMo, NiCo, NiFe, CoMn etc. Some of them showed high OER activity and stable in electrolyte.
Hematite (α-Fe2O3) is one of the best photoanodes due to its band gap (Eg = ~2.2 eV), chemical stability, abundance and cost. However, the reported efficiencies of hematite are notoriously lower than the predicted value, mainly due to the short photo-generated charge carriers lifetime (< 10ps) and short hole diffusion length (2 – 4 nm). The slow oxidation process limits the solar-to-fuel energy conversion efficiency. Catalytic surface modification plays a crucial role to lower the overpotential required for a given redox reaction to take place, and in some cases promotes separation and diffusion of carrier species.
Other narrow bandgap semiconductor, eg BiVO4 and metal sulfide.
BiVO4 has a bandgap energy of ~2.4 eV and a band structure that is well-suited for potential use as a photoanode in solar water splitting, but it suffers from poor electron-hole separation. Nanostructuring or doping with Mo or W can improve the charge separation of BiVO4 photoanode.
In addition, with the development of electron and hole conducting material, eg TiOx, NiOx and NbOx, the corrosion of traditional narrow bandgap semiconductors, eg metal sulfide or phosphide, is greatly improved. Thus these materials with suitable band position can be re-considered as candidate for tandem PEC.