Alternatives to Water Photooxidation for Photoelectrochemical Solar Energy Conversion and Green H₂ Production

Abstract

Photoelectrochemical (PEC) water splitting is considered a promising technology to produce renewable hydrogen, a clean fuel or energy carrier to replace conventional carbon‐based fossil‐fuel sources. Nevertheless, the overall solar‐to‐hydrogen efficiency and the cost‐effectiveness of this technology are still unsatisfactory for practical implementation. This can be primarily attributed to the sluggish kinetics of the anodic oxygen evolution reaction (OER) and the relatively low economic value of cogenerated O2 production. Over the past decades, there are extensive efforts to explore more kinetically favorable photooxidation reactions, which coupled with hydrogen evolution reaction (HER) can simultaneously improve H2 production yield and produce higher valuable alternatives to conventional O2. This review aims to present recent progress on the alternative anodic choices to OER. Here, the fundamental of PEC water splitting and the critical components required for this system are first shortly summarized. Then the benefits and issues of alternative photooxidation reactions including photooxidation of water to hydrogen peroxide, chlorine, alcohol, 5‐hydroxymethylfurfural, or urea oxidation when combined with the concurrent HER, are reviewed and analyzed. This review is concluded by presenting a critical evaluation of the challenges and opportunities of these alternative HER‐coupled photooxidation reactions for solar energy production and environmental treatment.

Strategies for reducing the overpotential of one-dimensional Si nanostructured photoelectrodes for solar hydrogen production

“…To address this problem, replacing the OER reaction with other reactions with lower oxidation potential and faster reaction kinetics is an effective strategy to reduce the overpotential of PEC hydrogen production. 4,[177][178][179] Especially, coupling HER with some organic reactions that produce highvalue chemicals can reduce the overpotential while lowering the cost of hydrogen production. 180,181 Although this strategy has not yet been applied in 1D Si nanostructured photoelectrodes, we believe it would be an effective way to reduce the overpotential of 1D Si nanostructured photoelectrodes for solar hydrogen production and reduce the cost of hydrogen production, which would help to improve the competitiveness of solar hydrogen production technology compared with the conventional technologies.…”

Suppression of Undesired Losses in Organometal Halide Perovskite‐Based Photoanodes for Efficient Photoelectrochemical Water Splitting

“…[1][2][3][4] However, achieving the high-efficiency solar H 2 production by PEC water splitting is still challenging. [5,6] The main limitation to achieving high solar-to-hydrogen conversion efficiency in unassisted solar water splitting is the relatively lowefficiency of photoanodes compared with that of photocathodes. [7][8][9] Thus far, various materials have been investigated as candidates for photoanodes, including WO 3 , [10,11] Fe 2 O 3 , [12][13][14] BiVO 4 , [15][16][17][18] Ta 3 N 5 , [19][20][21] and Si.…”

A quaternary heterojunction nanoflower for significantly enhanced electrochemical water splitting

“…16–20 Therein, NiFe-LDH has attracted particular attention due to its superior OER activities. 21–28…”

“…[16][17][18][19][20] Therein, NiFe-LDH has attracted particular attention due to its superior OER activities. [21][22][23][24][25][26][27][28] Although LDH has tremendous advantages in energyrelated applications, there are still some inherent drawbacks, such as low electrical conductivity and structural collapse during the exfoliation process, which results in hectic OER kinetics and inferior long-term usage. [21][22][23] In order to overcome these disadvantages, researchers have recently developed various strategies, including anion exchange, coupling with conductive substrates, designing heterojunctions and creating vacancies.…”

“…[21][22][23][24][25][26][27][28] Although LDH has tremendous advantages in energyrelated applications, there are still some inherent drawbacks, such as low electrical conductivity and structural collapse during the exfoliation process, which results in hectic OER kinetics and inferior long-term usage. [21][22][23] In order to overcome these disadvantages, researchers have recently developed various strategies, including anion exchange, coupling with conductive substrates, designing heterojunctions and creating vacancies. [24][25][26][27][28] Among these, the engineering of heterogeneous interfaces consisting of two or more active building blocks is a feasible and increasingly popular approach.…”