Review of recent progress in unassisted photoelectrochemical water splitting: from material modification to configuration design

Abstract

Photoelectrochemical (PEC) energy conversion systems have been considered as a highly potential strategy for clean solar fuel production, simultaneously addressing the energy and environment challenges we are facing. Tremendous research efforts have been made to design and develop feasible unassisted PEC systems that can efficiently split water into hydrogen (H 2) and oxygen with only the energy input of sunlight. A fundamental understanding of the concepts involved in PEC water splitting and energy conversion efficiency enhancement for solar fuel production is important for better system design. This review gives a concise overview of the unassisted PEC devices with some state-of-the-art progress toward efficient PEC devices for future sustainable solar energy utilization.

Hybrid Photoelectrochemical Water Splitting Systems: From Interface Design to System Assembly

“…The bandgap of the electrode, must be relatively narrow to promote light absorption. To reduce photogenerated charge recombination and enhance charge transfer, bulk phase defects should be limited, and morphology should be engineered to shorten the transport length of photogenerated electrons and holes which favors 1D nanorods and 2D ultrathin nanostructures 12,17. To obtain appropriate interfacial energetics for charge transfer, p‐ or n‐type semiconductors are preferred as photocathodes or photoanodes.…”

“…However, it is intrinsically difficult to directly employ semiconductor electrodes for highly efficient and stable PEC water splitting because of the challenges faced, including: inhibiting electron–hole recombination, accelerating poor interfacial charge transfer, matching energy levels for feasible water redox reactions, and narrowing bandgaps for broad sunlight absorption, all to be integrated simultaneously 8. To overcome these obstacles, various strategies have been developed, such as composite formations, surface modification, etc 12,17. Of particular interest is the coupling of semiconductors with molecular complexes to form hybrid PEC systems in which semiconductor is used for light harvesting and the molecular complex serves as a catalyst for water redox reactions.…”

“…Numerous efforts have been utilized for developing high‐performance hybrid PEC water splitting systems in recent years 12,13,17,20. There have been a number of excellent reviews published in related fields, including dye sensitized PEC23,24 and hybrid photocatalytic molecular systems13,20 for water splitting.…”

“…[11] Their research led to an extended series of research efforts devoted to the development of high-efficiency PEC systems for water splitting. [12][13][14][15][16] The past few decades have seen the rapid development of PEC water splitting systems, including both semiconductor sensitized systems [12,17] and organic dye sensitized systems. [13,14,18] Among them, semiconductor sensitized systems have been widely investigated due to ease of preparation of semiconductors, good stability, broad spectral response, and relatively low cost.…”

“…[8] To overcome these obstacles, various strategies have been developed, such as composite formations, surface modification, etc. [12,17] Of particular interest is the coupling of semiconductors with molecular complexes to form hybrid PEC systems in which semiconductor is used for light harvesting and the molecular complex serves as a catalyst for water redox reactions. As an approach it offers: 1) charge separation in both the bulk and surface of semiconductor which can be enhanced due to the efficient charge transfer from semiconductor to the molecular complex; 2) the high atom utilization similar to single atoms for catalysis, tunable physicochemical properties (e.g., redox potential) due to the variations in the central metal atom and ligand modifications, and clear-cut reaction mechanisms investigated for the molecular complex; 3) semiconductor surfaces that can be modified and protected by molecular complexes; and 4) intrinsic large Photoelectrochemical (PEC) water splitting has attracted increasing attention due to its potential to mitigate energy and environmental issues.…”