Hybrid photoanodes comprising polymer-based light absorbers coupled to oxygen-evolving cocatalysts represent a promising, yes still underdeveloped, approach to photoelectrochemical splitting of water into hydrogen and oxygen. In this study, we investigate nickel oxide (NiO x ) nanoparticles as a water oxidation catalyst in hybrid photoanodes based on polymeric carbon nitride (CN x ) supported on electron-collecting mesoporous TiO2 support. The performance of the resulting TiO2–CN x /NiO x photoanodes is evaluated with respect to our previous results on hybrid TiO2–CN x photoanodes modified with IrO x and CoO(OH) x cocatalysts. The deposition of NiO x into TiO2–CN x photoanodes enhances significantly the photocurrent (from <8 μA to >250 μA cm–2 at 1.23 V vs. RHE) under visible light irradiation (λ > 420 nm, ∼200 mW cm−2) and triggers the photoelectrocatalytic oxygen evolution. No oxygen evolution was observed without a cocatalyst. As compared to photoanodes modified with IrO x or CoO(OH) x , the TiO2–CN x /NiO x photoanodes excel by the very negative photocurrent onset potential (0 V vs. RHE), which we ascribe to good hole-extracting properties of NiO x . However, the comparatively low Faradaic efficiencies for oxygen evolution (∼18%) and dramatically decreased operational stability of the photoanodes indicate that the extracted holes do not efficiently oxidize water to dioxygen, but instead accumulate in the NiO x particles and increase thus the oxidative photodegradation of the photoanodes. Our study highlights the fact that employing outstanding electrocatalysts like NiO x in photoelectrochemical water-splitting systems does not necessarily lead to satisfactory results, especially when the photoelectrode cannot be operated at optimal pH due to light absorber stability issues.

No abstract

Related mechanisms for the photocatalytic degradation of methyl orange and photocatalytic enhancement of Mo-doped Bi2WO6 are demonstrated.

Bismuth vanadate (BiVO 4 ) powder was synthesized by the microwave method. Bismuth nitrate pentahydrate (Bi(NO 3 ) 3 .5H 2 O) and ammonium vanadate (NH 4 VO 3 ) were used as the starting precursors with the mole ratio of 1:1. The mixed solution was stirred and adjusted the pH of solution to 7 with ammonium hydroxide (NH 4 OH). The yellow final solution was treated in the microwave with an irradiation power at 600, 700 and 800 Watt for 2, 4 and 6 min, respectively. The phase of BiVO 4 powder was identified by X-ray diffraction (XRD). The morphology and chemical composition of BiVO 4 powder were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS), respectively. The surface area of BiVO 4 powder was determined by Brunauer-Emmett-Teller analysis (BET).