Engineering BiVO₄ and Oxygen Evolution Cocatalyst Interfaces with Rapid Hole Extraction for Photoelectrochemical Water Splitting

Abstract

Tailoring the oxygen evolution cocatalyst (OEC)/BiVO4 interfaces with a hole transfer layer (HTL) is expected to suppress the interfacial charge recombination, thus achieving highly efficient photoelectrochemical (PEC) water splitting. Herein, Co3O4 nanoparticles are inserted between the NiOOH OEC and BiVO4 as an HTL for the design of NiOOH/Co3O4/BiVO4 photoanodes. A champion photoanode achieves a photocurrent density of 6.4 mA cm–2 at 1.23 V versus the reversible hydrogen electrode (RHE) under AM 1.5 G illumination (100 mW cm–2). Stable PEC water splitting is realized for up to 90 h. Being highly dispersed at the surfaces of BiVO4, the p-type Co3O4 nanoparticles form p–n junctions with BiVO4, thus providing an extra driving force for the extraction of the photogenerated holes from BiVO4 to the NiOOH OEC, which efficiently suppresses charge recombination at the BiVO4/NiOOH interfaces and accelerates the surface water oxidation kinetics. A charge separation efficiency of 95.6% and a surface charge transfer efficiency of 97.7% are achieved at 1.23 V vs RHE. The strategy is applicable to other OEC (e.g., MnO x and FeOOH)/BiVO4 photoanodes. This work may inspire the rational design of high-performance photoanodes for feasible solar energy conversion.

Development of ABO4‐type photoanodes for photoelectrochemical water splitting

“…Co 3 O 4 was found to act as an HTL inserted into the interface of BiVO 4 and NiOOH to form a photoanode with a charge separation efficiency up to 95.6% 236 . In addition, Co 3 O 4 , as a p‐type semiconductor, formed a p‐n junction with BiVO 4 , which provides additional driving force for the separation and migration of the photogenerated carriers.…”

Imperfect makes perfect: defect engineering of photoelectrodes towards efficient photoelectrochemical water splitting

“…183 We have recently reported the regulation of the electronic structure by introducing oxygen vacancies on cocatalysts. 11,150,184…”

“…A typical PEC cell is composed of two electrodes connected in series and immersed in an electrolyte, and at least one electrode should be a semiconductor to absorb sunlight. 11 PEC water splitting includes three main steps: (I) light absorption, (II) photogenerated electron–hole separation and migration, and (III) redox reactions that occur at the photoelectrode surface. 12 When the photoelectrode absorbs photons whose energy is greater than or equal to its own bandgap energy, the electrons in the valence band (VB) are excited to the conduction band (CB), and holes are generated in the VB.…”

Schiff Base Complex Cocatalyst with Coordinatively Unsaturated Cobalt Sites for Photoelectrochemical Water Oxidation

“…Photoelectrochemical (PEC) water splitting using semiconductor materials offers an attractive route to convert solar energy into clean fuels. , However, the water oxidation evolution on photoanode is the bottleneck limiting the PEC cells for commercial applications owing to the complicated four-electron transfer process. − The rate-determining step is the energetically uphill formation of O–O bonds with a large energy barrier originating from the sluggish oxygen evolution reaction kinetics . Therefore, the critical challenge is the development of photoanodes with high conversion efficiencies for O 2 generation and extensive efforts have been devoted to improve the performance of photoanodes. , Rational integration of oxygen evolution cocatalysts (OECs) on semiconductor photoanodes is regarded as an available strategy to accelerate the water oxidation reaction kinetics with enhanced PEC water splitting activity. − Developments of OECs have driven much research efforts, while transition metal (oxyhydr)­oxides and metal phosphate constructed by inorganic components have been the most extensively used OECs for PEC water splitting applications. − …”

“…Unfortunately, the decoration of as-documented inorganic OECs for water oxidation inevitably creates new interfaces in photoanodes with concomitant electron–hole recombination at the semiconductor/OECs interfaces for the following reasons: (i) new charge recombination sites, (ii) mismatch in interfacial energetics, and (iii) excessive electrical transfer resistance. ,, These drawbacks synchronously block the photoholes’ transport to the OECs for participating in water oxidation reaction thus limit the PEC water oxidation performance. − Therefore, it is highly desirable to construct strong interactions at the semiconductor/OECs interfaces to suppress charge recombination with facilitated charge transfer for efficient PEC water oxidation. − …”