Tuning Light‐Driven Water Oxidation Efficiency of Molybdenum‐Doped BiVO₄ by Means of Multicomposite Catalysts Containing Nickel, Iron, and Chromium Oxides

Abstract

Mo‐doped BiVO4 has emerged as a promising material for photoelectrodes for photoelectrochemical water splitting, however, still shows a limited efficiency for light‐driven water oxidation. We present the influence of an oxygen‐evolution catalyst composed of Ni, Fe, and Cr oxides on the activity of Mo:BiVO4 photoanodes. The photoanodes are prepared by spray‐coating, enabling compositional and thickness gradients of the incorporated catalyst. Two different configurations are evaluated, namely with the catalyst embedded into the Mo:BiVO4 film or deposited on top of it. Both configurations provide a significantly different impact on the photoelectrocatalytic efficiency. Structural characterisation of the materials by means of SEM, TEM and XRD as well as the photoelectrocatalytic activity investigated by means of an optical scanning droplet cell and in situ detection of oxygen using scanning photoelectrochemical microscopy are presented.

Importance of catalyst–photoabsorber interface design configuration on the performance of Mo-doped BiVO4 water splitting photoanodes

“…The behaviour of the Co 3 O 4 catalyst (Fig. 6b) is similar to previously observed behaviour reported for a multicomposite catalyst [13], where the configuration on top resulted in decreased activity due to deprivation of the photoabsorber of light. In contrast, the configuration incorporating the catalyst embedded in the semiconductor film increased the activity towards water oxidation as a result of decreased surface recombination and lowering of the Fermi level, as manifested by additional downward bending of the band edge.…”

“…On the other hand, the monometallic oxide Co 3 O 4 only exhibited enhanced photoelectrocatalytic activity when the catalyst was embedded into the Mo:BiVO 4 semiconductor film, while a decrease in the measured photocurrents was observed when Co 3 O 4 was deposited on the surface of Mo:BiVO 4 . This observation is in agreement with recently reported results where the evaluated catalyst was constituted of a mixture of three different single transition metal oxides [13]. As previously explained, this behaviour was the result of a blocking of the redox active centres for oxygen evolution or/and shielding photoabsorber from light when the catalyst was deposited on top of the semiconductor material, while increased activity was obtained after embedding the catalyst in the semiconductor film due to a downward band bending of the catalyst-modified Mo:BiVO 4 .…”

“…In a recent communication [13], significantly distinct behaviour of photoanodes modified with the same co-catalyst in two different configurations, with the co-catalyst either deposited on the surface of Mo:BiVO 4 or embedded inside a Mo:BiVO 4 film, was observed. However, in these studies, no general correlation between co-catalyst-modified photoanode architecture and performance could be definitively established owing to a small number of Mo:BiVO 4 and Ni, Fe, and Cr multicomposite co-catalysts studied.…”

“…It is therefore reasonable to envision that the efficiency of solar water splitting should be more favourable when electrocatalysts are used in combination with photoelectrodes. However, studies on photoelectrochemical water splitting where the photoanode is modified with various oxygen evolution reaction (OER) catalysts tend to yield results that are not easy to interpret [12][13][14][15][16][17]. Nonetheless, a notable requisite towards efficient photoanode/co-catalyst systems seems to be the existence of a certain compatibility between the photoanode material and the incorporated co-catalyst.…”

Discovery of High-Entropy Oxide Electrocatalysts: From Thin-Film Material Libraries to Particles

“…The electrocatalytic activity toward OER in alkaline electrolytes was evaluated using a high-throughput SDC . Due to the use of the automated setup, the same measurement conditions are maintained for measuring hundreds of MAs, allowing reliable comparison of electrochemical activity data between different MAs and MLs. ,,, All measured LSVs, 2D color-coded activity maps, and the comparison of the activity of the most similar compositions prepared at different temperatures as well as the most active hit compositions from different MLs can be found in Figures S11–S13, SI. The electrochemical activity of different MAs is compared using the current density at 1.7 V vs RHE.…”