A rigidly adhered nitrogen-doped BiVO4 photoanode with a narrow band gap energy (E g = 2.35 eV) for water oxidation was developed to attain the IPCE value of 35.1% at 440 nm which is among the highest reported values. This electrode provides a very stable photocurrent density of 3.3 mA cm–2 at 1.23 V vs RHE for a long term (at least 13.4 h) under visible light irradiation (100 mW cm–2).

Facile and scalable fabrication of α-Fe 2 O 3 photoanodes using a precursor solution containing Fe III ions and 1-ethylimidazole (EIm) in methanol was demonstrated to afford a rigidly adhered α-Fe 2 O 3 film with a controllable thickness on a fluorine-doped tin oxide (FTO) substrate. EIm ligation to Fe III ions in the precursor solution brought about high crystallinity of three-dimensionally well-interconnected nanoparticles of α-Fe 2 O 3 upon sintering. This is responsible for the 13.6 times higher photocurrent density (at 1.23 V vs reference hydrogen electrode (RHE)) for photoelectrochemical (PEC) water oxidation on the α-Fe 2 O 3 (w-α-Fe 2 O 3 ) photoanode prepared with EIm compared with that (w/o-α-Fe 2 O 3 ) prepared without EIm. The w-α-Fe 2 O 3 photoanode provided the highest charge separation efficiency (η sep ) value of 27% among the state-of-the-art pristine α-Fe 2 O 3 photoanodes, providing incident photon-to-current conversion efficiency (IPCE) of 13% at 420 nm and 1.23 V vs RHE. The superior η sep for the w-α-Fe 2 O 3 photoanode is attributed to the decreased recombination of the photogenerated charge carriers at the grain boundary between nanoparticles, in addition to the higher number of the catalytically active sites and the efficient bulk charge transport in the film, compared with w/o-α-Fe 2 O 3 .

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The catalytic aspect of a mononuclear Ru complex, [Ru(C8Otpy)(dcbpy)(OH)]− (1) (C8Otpy = 4′-octyloxy-2,2′:6′,2″-terpyridine, H2dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) on a mesoporous indium tin oxide (m-ITO) electrode was investigated by multi-potential-step chronocoulo(ampero)spectrometry (MPSCC(A)S) combined with in situ O2 evolution analysis. For the repetitive MPSCC(A)S measurement between 0.2 and 1.7 V vs Ag/AgCl, 39% of 1 recovered on the first back potential-step to 0.2 V, but 1 no longer recovered after the 4th back potential-step, although the in situ measured amount of O2 increased monotonously with time. XPS and Raman spectroscopic measurements reveal that 1 on the electrode pronouncedly undergoes the oxidative transformation to form the hydrated RuO2 as the alternative catalysts under the high applied potential of 1.7 V. The RuV=O state is more active for water oxidation than the RuIV=O state but could be prone to transform to hydrated RuO2. This tells us that the low applied potential but enough for formation of the RuIV=O species is important for 1 to work stably as a molecular catalyst on the electrode.