Boosting the solar water oxidation performance of a BiVO₄ photoanode by crystallographic orientation control

Abstract

A BiVO4 with a preferred [001] orientation and exposed {001} facets were grown epitaxially on FTO via a laser ablation, achieving the state-of-the-art photoelectrochemical performance for solar water-oxidation.

Stepping towards Solar Water Splitting: Recent Progress in Bismuth Vanadate Photoanodes

“…Besides the ordered porosity, nanomaterials with low crystal symmetry often exhibit anisotropic properties, in which specific exposed crystal facets and crystallographic orientation can effectively tune the physical and chemical properties resulting in highly reactive sites, excellent intrinsic charge transport and particular photo-induced holes/electrons rich surface. [38,46,73,74] Li et al discovered a novel type of spatial separation of photoinduced electrons and holes among the (010) and (110) crystal facets in BiVO 4 as presented in Figure 7a, which allowed selective deposition of reduction and oxidation co-catalysts on the (010) and (110) facets, respectively, leading to a much higher photoactivity for solar water splitting compared to the randomly distributed co-catalysts. [72,75] This study suggests the importance of precise control of the co-catalyst loading on the relevant exposed crystal facets for oxidation and reduction reactions, which is an effective means of mitigating the surface charge recombination.…”

“…[37] Recently, Han et al realized a preferred (001) growth orientation of pristine BiVO 4 on FTO substrate by laser ablation, reaching a photocurrent density of 3.9 mA/cm 2 at 1.23 vs. RHE, which is the highest record for pristine BiVO 4 photoanodes for solar water oxidation without co-catalysts. [38] This enhanced PEC performance was attributed to the selectively exposed crystal facet of BiVO 4 , which enabled photo-induced holes to transport along and react at (001) with excellent intrinsic charge transport properties and surface reactivity ( Figure 7c). These distinct design and preferential crystallographic orientation growth can successfully overcome the inherent limitations associated with BiVO 4 , such as sluggish oxygen evolution reaction kinetics and poor charge transport and collection by reducing surface, bulk, and interfacial charge recombination.…”

“…[30,62,107] In order to promote the OER process, typical oxygen evolution co-catalysts (OECs), such as transition metal oxides (RuO 2 , IrO 2 , CoO x , MnO x ), (oxy)hydroxide (NiOOH/FeOOH, FeOOH/CoOOH), phosphide/phosphate (CoP/ CoPi), have been widely studied and employed to deposit on the surface of photoanodes. [15,38,40,53,72,108] This subsection gives an overview on some co-catalysts and discusses the effects of co-catalysts.…”

“…[109] Since then, CoPi has been extensively applied as a cocatalyst on photoanodes for solar water oxidation. [37,38,50] Some studies compared the differences between photo-assisted electrodeposition and electrodeposition methods. [40,110] For example, Zhong et al demonstrated that photo-assisted electrodeposition provides a more uniform distribution of CoPi on photoanodes than those obtained by electrodeposition.…”

Current perspectives in engineering of viable hybrid photocathodes for solar hydrogen generation

“…Indeed, while several photocathodes can offer a short-circuit photocurrent j SC of few-tens mA cm −2 (see following sections and table 1), most of the reported photoanodes showed low j SC of 1 ÷ 4 mA cm −2 or even less. The record of 6.1 mA cm −2 was reported for a BiVO 4 /CoPi photoanode very recently [18]. Other than the H 2 production yield, a PEC device is expected to operate continuously for over 1000 h. The latter demand is critical in order to make solar H 2 competitive with that produced from the natural gas.…”