Strategies for Semiconductor/Electrocatalyst Coupling toward Solar‐Driven Water Splitting

Abstract

Hydrogen (H2) has a significant potential to enable the global energy transition from the current fossil‐dominant system to a clean, sustainable, and low‐carbon energy system. While presently global H2 production is predominated by fossil‐fuel feedstocks, for future widespread utilization it is of paramount importance to produce H2 in a decarbonized manner. To this end, photoelectrochemical (PEC) water splitting has been proposed to be a highly desirable approach with minimal negative impact on the environment. Both semiconductor light‐absorbers and hydrogen/oxygen evolution reaction (HER/OER) catalysts are essential components of an efficient PEC cell. It is well documented that loading electrocatalysts on semiconductor photoelectrodes plays significant roles in accelerating the HER/OER kinetics, suppressing surface recombination, reducing overpotentials needed to accomplish HER/OER, and extending the operational lifetime of semiconductors. Herein, how electrocatalyst coupling influences the PEC performance of semiconductor photoelectrodes is outlined. The focus is then placed on the major strategies developed so far for semiconductor/electrocatalyst coupling, including a variety of dry processes and wet chemical approaches. This Review provides a comprehensive account of advanced methodologies adopted for semiconductor/electrocatalyst coupling and can serve as a guideline for the design of efficient and stable semiconductor photoelectrodes for use in water splitting.

Insight into the Transition‐Metal Hydroxide Cover Layer for Enhancing Photoelectrochemical Water Oxidation

“…It has been demonstrated in recent years that coupling TMH with semiconductor (n‐Fe 2 O 3 , [11, 12] n‐BiVO 4 , [13, 14] WO 3 , [15] etc.) to get integrated photoelectrodes is a smart strategy for improving PEC performance [16, 17] . Based on these reported literatures, the reasons for PEC performance enhancement can be summarized as the following aspects: 1) the TMH (referred as true catalyst in the dark) expedites the reaction kinetics by reducing reaction overpotentials; [12, 17] 2) these catalysts act as a spectator (or a passivating layer), which can passivate defects on the semiconductor surface and thus reduce the recombination of electrons and holes photogenerated; [18–20] 3) these typical TMH can collect or store photogenerated holes and drive water oxidation [12, 21] .…”

“…to get integrated photoelectrodes is a smart strategy for improving PEC performance [16, 17] . Based on these reported literatures, the reasons for PEC performance enhancement can be summarized as the following aspects: 1) the TMH (referred as true catalyst in the dark) expedites the reaction kinetics by reducing reaction overpotentials; [12, 17] 2) these catalysts act as a spectator (or a passivating layer), which can passivate defects on the semiconductor surface and thus reduce the recombination of electrons and holes photogenerated; [18–20] 3) these typical TMH can collect or store photogenerated holes and drive water oxidation [12, 21] . Despite these understandings from charge separation or surface catalytic reaction have made a huge contribution to PEC water splitting within certain range, the fate of photogenerated holes at the interfaces among semiconductor/TMH/electrolyte has not yet been reported in detail.…”

Atomic Layer Deposition for the Photoelectrochemical Applications

“…This provides the deposition of semiconductors onto nanostructured substrates and the fabrication of highly nanostructured heterojunction‐device ( Figure a). Nanostructured materials are of particular interest in PEC devices as they offer a higher surface area for catalyst dispersion [ 25 ] as well as some specific adsorption and transport properties. [26,27] The materials employed as light absorbers in PEC devices together with the deposition parameters, are presented in Table 1 .…”

Enhancing Charge Separation through Oxygen Vacancy‐Mediated Reverse Regulation Strategy Using Porphyrins as Model Molecules

“…Unfortunately, severe charge recombination often occurs in semiconductor light‐absorbers, which largely impedes their further applications in the field of solar energy conversion and utilization. [ 4–6 ] Up to now, substantial efforts have been devoted to enhancing charge separation by heterostructure construction, [ 7 ] co‐catalyst loading, [ 8–10 ] element doping [ 11 ] and polarization, [ 12 ] among which coupling co‐catalysts with semiconductors is a common and widespread method to improve the sluggish reaction kinetics [ 13 ] or influence the band bending of semiconductor to enhance charge separation. [ 14 ] However, the introduction of co‐catalysts may cause unwanted light absorption and increase the possibility of recombination of photogenerated electrons and holes at the semiconductor/co‐catalyst junction.…”

“…[ 14 ] However, the introduction of co‐catalysts may cause unwanted light absorption and increase the possibility of recombination of photogenerated electrons and holes at the semiconductor/co‐catalyst junction. [ 13,15 ] Therefore, developing highly efficient regulation methods is quite desirable and imperative for improving charge separation.…”