Photoelectrocatalytic Water Splitting: Significance of Cocatalysts, Electrolyte, and Interfaces

Abstract

The efficiency of photoelectrocatalytic (PEC) water splitting is limited by the serious recombination of photogenerated charges, high overpotential, and sluggish kinetics of surface reaction. Herein we describe the recent progress on engineering the electrode–electrolyte and semiconductor–cocatalyst interfaces with cocatalysts, electrolytes, and interfacial layers (interlayers) to increase the PEC efficiency. Introducing cocatalysts has been demonstrated to be the most efficient way to lower the reaction barrier and promote charge injection to the reactants. In addition, it has been found that electrolyte ions can influence the surface catalysis remarkably. Electrolyte cations on the surface can influence the water splitting and backward reactions, and anions may take part in the proton transfer processes, indicating that fine-tuning of the electrolyte parameters turns out to be an important strategy for enhancing the PEC efficiency. Moreover, careful modification of the interface between the cocatalysts and the semiconductor via suitable interlayers is critical for promoting charge separation and transfer, which can indirectly influence the surface catalysis. The mechanisms of surface catalysis are assumed to involve transfer of photogenerated holes to the surface active sites to form high-valent species, which then oxidize the water molecules. Many key scientific issues about the generation of photovoltage, the separation, storage, and transfer of carriers, the function of cocatalysts, the roles of electrolyte ions, and the influences of other parameters during PEC water splitting will be discussed in detail with some perspective views.

Solar‐to‐Hydrogen Energy Conversion Based on Water Splitting

“…[82] The first challenge in the PEC cells is to find semiconductor materials with proper band structures and efficient visible light absorption, which are also the major concerns of photocatalysts as introduced in the above section. [83] In summation, the research in PEC water splitting needs the contributions not only from chemists and material scientists but also from engineers. The overpotential of water splitting, especially for the kinetically challenging water oxidation, is usually high.…”

Rational Design and Construction of Cocatalysts for Semiconductor‐Based Photo‐Electrochemical Oxygen Evolution: A Comprehensive Review

“…Once the above system is exposed under light (Figure 4b), the surface potential of the photoanode and the H + /H 2 potential will be reduced. [17] Copyright 2016, American Chemical Society. .…”

“…According to Ding et al [17] and Yang et al, [80] E onset under irradiation will be influenced by two factors: open-circuit photovoltage (V ph ) and kinetic overpotential (η k ), as Equation (4) shows. Sci.…”

“…It is reported that a Co-based molecular catalyst was coated onto an amorphous silicon photoanode which carried out a water splitting reaction efficiency of 4.7% for a wired configuration and 2.5% for a wireless configuration Adv. [17] Therefore, tackling this shortcoming is indispensable if we want to further investigate their functions as OER cocatalysts. 2019, 6, 1801505 Figure 18.…”

“…Su et al [13] and Hong et al [14] proposed that the heterojunction formed between interface of WO 3 and BiVO 4 was conducive to charge transfer and recombination suppression. [17] Besides, the methods to incorporate cocatalysts with photoelectrodes such as electrodeposition or photo-electrodeposition are facile and easy to implement. [15] Yang et al rationally synthesized nitrogendoped ZnO nanowire arrays as photoanodes and the obtained photocurrent of ZnO:N increased by an order of magnitude than that of bare ZnO.…”