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The water oxidation half-reaction at anodes is always considered the rate-limiting step of overall water splitting (OWS), but the actual bias distribution between photoanodes and cathodes of photoelectrochemical (PEC) OWS cells has not been investigated systematically. In this work, we find that, for PEC cells consisting of photoanodes (nickel-modified n -Si [Ni/ n -Si] and α-Fe2O3) with low photovoltage (V ph < 1 V), a large portion of applied bias is exerted on the Pt cathode for satisfying the hydrogen evolution thermodynamics, showing a thermodynamics-controlled characteristic. In contrast, for photoanodes (TiO2 and BiVO4) with V ph > 1 V, the bias required for cathode activation can be significantly reduced, exhibiting a kinetics-controlled characteristic. Further investigations show that the bias distribution can be regulated by tuning the electrolyte pH and using alternative half-reaction couplings. Accordingly, a volcano plot is presented for the rational design of the overall reactions and unbiased PEC cells. Motivated by this, an unbiased PEC cell consisting of a simple Ni/ n -Si photoanode and Pt cathode is assembled, delivering a photocurrent density of 5.3 ± 0.2 mA cm−2. [ABSTRACT FROM AUTHOR]

High‐efficient photoelectrocatalytic direct ammonia oxidation reaction (AOR) conducted on semiconductor photoanodes remains a substantial challenge. Herein, we develop a strategy of simply introducing ppm levels of Cu ions (0.5–10 mg/L) into NH3 solutions to significantly improve the AOR photocurrent of bare BiVO4 photoanodes from 3.4 to 6.3 mA cm−2 at 1.23 VRHE, being close to the theoretical maximum photocurrent of BiVO4 (7.5 mA cm−2). The surface charge‐separation efficiency has reached 90 % under a low bias of 0.8 VRHE. This AOR exhibits a high Faradaic efficiency (FE) of 93.8 % with the water oxidation reaction (WOR) being greatly suppressed. N2 is the main AOR product with FEs of 71.1 % in aqueous solutions and FEs of 100 % in non‐aqueous solutions. Through mechanistic studies, we find that the formation of Cu−NH3 complexes possesses preferential adsorption on BiVO4 surfaces and efficiently competes with WOR. Meanwhile, the cooperation of BiVO4 surface effect and Cu‐induced coordination effect activates N−H bonds and accelerates the first rate‐limiting proton‐coupled electron transfer for AOR. This simple strategy is further extended to other photoanodes and electrocatalysts. [ABSTRACT FROM AUTHOR]

Epoxides are significant intermediates for the manufacture of pharmaceuticals and epoxy resins. In this study, we develop a Br−/BrO− mediated photoelectrochemical epoxidation system on α-Fe2O3. High selectivity (up to >99%) and faradaic efficiency (up to 82 ± 4%) for the epoxidation of a wide range of alkenes are achieved, with water as oxygen source, which are far beyond the most reported electrochemical and photoelectrochemical epoxidation performances. Further, we can verify that the epoxidation reaction is mediated by Br−/BrO− route, in which Br− is oxidized non-radically to BrO− by an oxygen atom transfer pathway on α-Fe2O3, and the formed BrO− in turn transfers its oxygen atom to the alkenes. The non-radical mediated characteristic and the favorable thermodynamics of the oxygen atom transfer process make the epoxidation reactions very efficient. We believe that this photoelectrochemical Br−/BrO−-mediated epoxidation provides a promising strategy for value-added production of epoxides and hydrogen. Alkene epoxidation, whose products are important intermediates for the manufacture of pharmaceuticals and epoxy resins, has attracted extensive attention. Unlike the conventional electrochemical Br−/Br2-mediated epoxidation, here the authors report a photoelectrochemical Br−/BrO−- mediated system to achieve efficient epoxidation performance on α-Fe2O3. [ABSTRACT FROM AUTHOR]

The sluggish H2O oxidation kinetics on photoanodes severely obstructs the overall solar‐to‐energy efficiency of photoelectrochemical (PEC) cells. Herein, we find a 10 to 55‐fold increase of photocurrent by conducting ammonia oxidation reaction (AOR) on hematite (α‐Fe2O3) photoanodes under near‐neutral pH (9–11) and moderate applied potentials (1.0–1.4 VRHE) compared to H2O oxidation. By rate law analysis and operando spectroscopic studies, we confirm the non‐radical nucleophilic attack of NH3 molecules on high‐valent surface Fe−O species (e.g. FeIV=O) and Fe−N species that produces NOx− and N2, respectively, which overwhelms the nucleophilic attack of H2O on surface FeIV=O and contributes to a high Faradaic efficiency of above 80 % for AOR. This work reveals a novel non‐radical nucleophilic attack strategy, which is significantly different from the conventional indirect radical‐mediated AOR mechanism, for the rational design of high‐performance AOR photoelectrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrathin CuNi 2 Al-LDH with rich Cu(I) active sites is fabricated. • Electron transfer from Ni to Cu in the CuNi 2 Al-LDH induces the production of Cu(I). • The co-exist of Ni and Cu ions enhance the light harvesting ability of LDH. • Ni atoms as electron-transfer mediators accelerate the Cu(II)/Cu(I) cycling. • Possible photo-Fenton-like synergistic reaction mechanism is proposed. The Cu-based photo-Fenton-like process stands out as a promising technology for water decontamination, but its catalytic efficiency for refractory organic pollutants removal still suffers from shortage of Cu(I) supply in the activation of H 2 O 2. Herein, we, for the first time, developed ultrathin nanosheets of Cu(I)-enrich CuNi 2 Al layered double hydroxides (CuNi 2 Al-LDH) with fast electron transfer rate to achieve superior visible-light-driven photo-Fenton catalytic performance. In the brucite-like sheets of LDH, the electron donation effect of Ni enabled the electron transfer from Ni to Cu, resulting in generation of 62.9 % Cu(I) content, which provided abundant Cu(I) active sites for Fenton-like reaction. Notably, the coexistence of Ni and Cu ions in the nanosheets significantly enhanced the visible-light harvesting ability by d-d transitions, thereby boosting the production of photogenerated carriers. More importantly, the Ni sites with excellent electroactivity served as electron-transfer mediators to remarkably promote the photogenerated carriers charge separation and photogenerated electrons transfer, leading to nearly 20 times improvement in the photocurrent density of CuNi 2 Al-LDH in comparison to the Ni-free LDH, which greatly expedited the Cu(II)/Cu(I) cycle and promoted H 2 O 2 activation. Benefiting from these advantages, CuNi 2 Al-LDH could degrade 100 % of phenol, tetracycline (TC) and dyes within 30 min at room temperature through the synergy effect of photocatalysis and Fenton oxidation, and the reactive oxygen species •OH, •O 2 − and 1O 2 contributed 44.2 %, 12.9 % and 37.7 % to the degradation of pollutants, respectively. This study provides an ingenious strategy to the rational design of on-demand multifunctional catalysts for advanced water remediation. [ABSTRACT FROM AUTHOR]