An overview of co‐catalysts on metal oxides for photocatalytic water splitting

Abstract

Hydrogen (H 2 ) generation through photoelectrochemical (PEC) water splitting is a promising approach to reducing energy crises and associated environmental problems. Among currently available semiconductors, 2D nanostructured metal oxides have attracted wide interest in PEC applications because of their low-cost synthesis routes, stability in aqueous media, unique configuration and features, and favorable band edge positions. However, metal oxides still suffer from the severe recombination of photogenerated charge carriers and the low consumption of visible light. One solution is to introduce co-catalysts to enhance photocatalytic H 2 generation by improving charge separation and transfer, extending light absorption, and lowering the activation energy. This review summarizes the fundamentals and recent developments of co-catalysts on metal oxides which can be classified into the following categories: metal cocatalysts, metal sulfide co-catalysts, metal hydroxide co-catalysts, metal phosphide co-catalysts, carbon-based co-catalysts, and dual co-catalysts. Charge transfer mechanisms of co-catalysts on metal oxides in photocatalytic H 2 generation and present future trends for co-catalysts and strategies in enhancing PEC water splitting are also presented.

Development of Sulfur-Doped Graphitic Carbon Nitride for Hydrogen Evolution under Visible-Light Irradiation

“…Then, in the oxygen-free photocatalytic system, the photogenerated holes are consumed by the electron donor and the photoinduced electrons are trapped near the g-C 3 N 4 surface, probably forming N defect sites in place for proton ( + H) reduction (in the absence of co-catalyst such as Pt) [ 84 , 85 ]. The Pt co-catalyst on the CN surface might act as a sink (already proven for various other semiconductors [ 86 , 87 , 88 ]) for the photogenerated electrons, thus improving the electron-hole separation [ 85 , 89 ]. Moreover, it has been proposed that noble-metal co-catalyst works as an active site for the formation of hydrogen molecule, e.g., in the case of Ni/Pd-co modified titania samples [ 90 ].…”

Photocatalytic Synthesis of Materials for Regenerative Medicine Using Complex Oxides with β-pyrochlore Structure

“…Their application makes it possible to avoid the use of auxiliary and intermediate substances in the synthesis, reduces the number of process steps, etc. Different photocatalytic reactions, such as water splitting [ 3 , 4 , 5 , 6 , 7 ], the degradation of organic substances in aqueous solutions [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ], and polymerization [ 21 , 22 , 23 , 24 ], have been intensively studied. The use of photocatalysis for obtaining biomedical materials based on natural polymers is an especially attractive area of research.…”

Single transition metal atom centered clusters activating semiconductor surface lattice atoms for efficient solar fuel production

“…6,7 Noble metals, such as Pt and Pd, generally possess large work functions which facilitate capturing photogenerated electrons from semiconductor photocatalysts, and appropriate H intermediate adsorption affinities desired for catalysing the hydrogen evolution reaction, and thus are frequently loaded onto the surface of light harvesting semiconductors to accelerate the rate of hydrogen production. 8,9 However, the further widespread utilization of these noble metals for solar-to-fuel conversion has been greatly restricted by their extreme scarcity and high price.…”

“…oxides, hydroxides, sulphides, phosphides, and carbides), nanocarbons, and articial organometallic molecules, have been proven to be effective for hydrogen production, even with performance surpassing those of noble metals. 9,10,13 Nonetheless, all these ndings rely to a great extent on trial-and-error and/or combinatorial approaches, 14,15 with little attention being paid to the investigation of the underlying structure-activity relationships. 16 The real active state of the cocatalyst, the location of the reaction site and its exact structure, as well as the fundamental operating mechanism, thus are all not exactly known, severely impeding the further rational design of efficient hydrogen production cocatalysts.…”