No abstract

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 .

Nickel-based materials are promising electrocatalysts for an alkaline oxygen evolution reaction (OER), which is indispensable for developing water-splitting systems to produce hydrogen as a carbon-neutral fuel. Different NiO x films adhered rigidly on nickel foam (NF) and fluorinedoped tin oxide substrates were prepared via a mixed metal-imidazole casting method from precursor solutions containing Ni salts with four different counter anions of SO 4 2− , NO 3 − , Cl − , and CH 3 COO − (Ac) in methanol/1methyimidazole mixed solvents (3:1) followed by calcination at 450 °C. The counter ions of Ni salts are significantly influential on the structure and characteristics of the formed NiO x films. In the case of the film (SO 4 -NiO x ) prepared from the NiSO 4 precursor, an amorphous Ni III O x nanosheet film was formed in contrast to face-centered cubic Ni II O crystalline nanoparticle films formed using the other precursors, under the same conditions. The special characteristics of the SO 4 -NiO x film are caused by the inhibition effect of the SO 4 2− ions on the thermochemical formation of Ni II O from the precursor complex, leading to the formation of a Ni III O x intermediate. The SO 4 -NiO x /NF electrode demonstrated superior OER performance with an overpotential, η 10 = 228 mV at a current density of 10 mA cm −2 in alkaline KOH solutions, which is lower by 145∼165 mV than those (η 10 = 373∼393 mV) of the other NiO x /NF electrodes. The OER performance of the SO 4 -NiO x /NF electrode compares advantageously with that of state-of-the-art Ni-based anodes reported to date.

Platinum-based materials are utilized as efficient catalysts for hydrogen evolving reaction (HER) from water due to its optimal binding ability with hydrogen atom. A platinum (w-Pt) film adhered rigidly deposited...