Transition‐Metal‐Based Cocatalysts for Photocatalytic Water Splitting

Abstract

Recently, semiconductor‐based photocatalytic water splitting has been extensively studied as a promising strategy for converting solar energy into carbon‐neutral and clean H2 fuel. However, the lack of sufficient active sites for surface redox reactions generally results in unsatisfactory photocatalytic water splitting performances over semiconductors. For this problem, cocatalyst provides an encouraging solution and is of great significance in improving photocatalytic performance. Noble metals and their derivatives are mostly utilized as efficient cocatalytic components, but their scarcity and expensiveness severely hamper large‐scale applications. Thereby, the utilization of noble‐metal‐free cocatalysts has aroused immense research attention. Owing to the facile availability, low cost, large abundance, high stability, and efficient performance, transition‐metal‐based materials have been developed as desirable candidates in the photocatalytic water splitting water splitting process. This review gives an outline of some recent advances in the active transition‐metal‐based water splitting cocatalysts. First, the fundamentals of transition‐metal‐based cocatalysts are presented, including the classification, function mechanisms, loading methods, modification strategies, and design considerations. Second, the various cases of depositing reduction cocatalysts, oxidation cocatalysts, and reduction–oxidation dual cocatalysts for water splitting are further discussed. Finally, the crucial challenges and possible research directions of transition‐metal‐based cocatalysts for photocatalytic water splitting are proposed.

Point‐to‐face contact heterojunctions: Interfacial design of 0D nanomaterials on 2D g‐C3N4 towards photocatalytic energy applications

“…67 Certainly, these drawbacks can be simultaneously addressed by depositing suitable reduction cocatalysts on the surface of g-C 3 N 4 to reduce the activation energy of the process, achieve better charge separation and transfer, enhance photocatalyst stability, and speed up the sluggish catalytic performance of numerous surface reduction reactions. 109,110 The loading of cocatalysts generally serves two purposes: to store electrons, allowing the photoexcited carriers to be efficiently separated, 111 and promote reduction or oxidation active sites, which reduces the overpotential and charge-transfer barrier. 87 0D cocatalysts are often used to enhance the overall photocatalytic activity of 2D g-C 3 N 4 and supply active sites for redox reactions.…”

Visible-Light Photocatalytic Water Splitting and Norfloxacin Degradation by Reduced Graphene Oxide-Coupled MnON Nanospheres

“…Pioneering research efforts toward photocatalytic water splitting using TiO 2 as a semiconductor were reported by Fujishima and Honda . Subsequently, numerous research efforts involving a multitude of semiconductors have been aimed at photocatalytic water splitting. − The overall water splitting mechanism proceeds as follows: the photocatalyst upon absorbing photonic energy greater than its band gap energy generates bulk electron–hole pairs that migrate to the surface without recombination to facilitate reduction and oxidation of water, respectively, to yield H 2 and O 2 . For photocatalytic water splitting, the bottom of the conduction band must be higher than the reduction potential of H + to H 2 (0 V vs NHE) and the top of the valence band must be lower than the oxidation potential (1.23 V vs NHE) .…”

Plasmonic Titanium Nitride/g-C3N4 with Inherent Interface Facilitates Photocatalytic CO2 Reduction

“…Although various g-C 3 N 4 -based materials that are capable of reducing CO 2 have been developed, the light absorption of bulk g-C 3 N 4 needs further improvement as its absorption edge only extended to 420 nm, and thus does not overlap the entire visible-light region. Numerous efforts have been made to improve the light absorption of g-C 3 N 4 -based photocatalysts, such as doping, , copolymerization, − and coupling with small band gap semiconductors. − In recent years, plasmonic materials have received tremendous attention as they possess surface plasmon resonance (SPR) in the visible-light region. , The plasmonic nanoparticles (NPs) can convert solar light into hot electrons through the surface plasmon decay . Also, the light absorption of plasmonic NPs can be tuned flexibly by changing their shape, size, or composition. − Among other plasmonic metals, gold nanoparticles (Au NPs) are the most investigated owing to the wide range of synthetic procedures with different sizes and shapes with a thorough understanding of their plasmonic behavior. ,− However, the high cost, low thermal stability, and scarcity of gold remain challenges for developing plasmonic gold-based photocatalysts.…”