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Metal oxyhydroxide (MOOH) through irreversible reconstructed fabrication from transition metal compounds are highly efficient oxygen evolution reaction (OER) electrocatalysts but face limits from adsorption energy scaling relationship and sluggish deprotonation kinetics. Herein, we present Fe-doped nickel hydrogen cyanamide (Ni 0.8 Fe 0.2 -HC), which is rapidly surface reconstructed into Ni 0.8 Fe 0.2 (OOH)-HC after OER. In-situ Raman spectroscopy and density functional theory (DFT) calculations, revealed that under OER conditions, -HNCN- converts into -NCN- ligand incorporating its abundant and uniform distribution across the active sites. DFT calculations further indicate that Fe predominantly acts as the active site, with -NCN- ligands contribute to the OER by facilitating the deprotonation of *OH in the rate-determining step (RDS), acting effectively as proton acceptor. The ensemble effect between Fe and -NCN- ligand forms the foundation of the exceptional electrocatalytic performance of Ni 0.8 Fe 0.2 (OOH)-HC (190 mV at 20 mA·cm−2). This discovery offers insights for designing innovative MOOH pre-catalysts to enhance OER efficiency. [Display omitted] • Pre-catalyst Ni0.8Fe0.2-HC is prepared by a one-step method. • Ni0.8Fe0.2(OOH)-HC with proton acceptor is in-situ produce by rapid reconstruction. • In-situ generation of -NCN- makes it uniformly distributed across the active sites. • Ni0.8Fe0.2(OOH)-HC exhibit excellent OER performance (190 mV at 20 mA∙cm-2). [ABSTRACT FROM AUTHOR]

Photocatalytic water oxidation suffers from sluggish kinetics and remains the bottleneck for water splitting. Here, using CeO 2 nanorods as model photocatalyst we studied the critical role of oxygen vacancies in photocatalytic water oxidation. First CeO 2 nanorods with similar morphology but different concentration of oxygen vacancies were fabricated by one-step hydrothermal method with in-situ reducing treatment. The optical absorption, charge transfer efficiency, and photocatalytic activity in oxygen generation were found closely dependent on the concentration of oxygen vacancies. Then density functional theory calculations were conducted to unveil the role of oxygen vacancies and understand the water oxidation mechanism. It was found the presence of oxygen vacancies narrows the bandgap and modulates the electronic structure for accelerating the charge transfer, in good agreement with the experimental observations. The overall oxygen generation pathway was screened and the oxygen vacancies were found to lower the barrier energy for the rate limiting step of O O bond formation and restrain the reverse reaction of O and H, thus the O 2 generation kinetics on oxygen-defective CeO 2 are improved significantly. This study provides in-depth understanding on the critical role of oxygen vacancies in photocatalytic water oxidation and is helpful for designing highly efficient photocatalyst to overcome the bottleneck of water splitting. [ABSTRACT FROM AUTHOR]

The utilization of solar energy into photoelectrochemical (PEC) water splitting is a popular approach to store the sustainable energy and minimize the dependence of fossil fuels. Herein, multi-layer BiVO 4 films were synthesized by multi-cycle electrodeposition following by annealing at high temperature. Multi-layer BiVO 4 films have monoclinic scheelite structure, and the morphology is changed from densely compact film to sponge-like network, and then bulk structure with the increase of electro-deposited layers. X-ray photoelectron spectra indicate the presence of abundant oxygen vacancies and V 4+ species in multi-layer BiVO 4 , especially for 3-layer one. For visible-light PEC performance, 3-layer BiVO 4 shows the highest photocurrent among the samples, i.e. up to 5.80 mA/cm 2 in sulfite oxidation and 1.79 mA/cm 2 in water splitting at 1.23 V versus a reverse hydrogen electrode (RHE) under 1 sun irradiation (100 mW/cm 2 ), with very high IPCE achieved nearly 83% and 25% (at 420 nm), respectively. The extremely high PEC performance of 3-layer BiVO 4 is attributed to its morphology of sponge-like network and the modulated band structure by the oxygen vacancies and V 4+ species. Moreover, the multi-layer BiVO 4 also shows very high photostability. This work provides a multi-layer-construction method for highly visible-light-active PEC anodes for practical applications. [ABSTRACT FROM AUTHOR]

Direct Z-scheme photocatalyst, which enables efficient charge separation and retains high redox ability, is promising material for visible-light-driven hydrogen evolution. Here we developed a one-step solvothermal method to fabricate direct Z-scheme CdS/CdWO 4 composite via treating W 18 O 49 with CH 3 CSNH 2 and Cd(CH 3 COO) 2 . By controlling the dosage of Cd(CH 3 COO) 2 , CdS nanoparticles decorated CdWO 4 nanowires (CS-2) is synthesized. UV–vis DRS and XPS spectra demonstrate that the CdWO 4 possesses a large amount of oxygen vacancies, which help to form ohmic contact and broaden light absorption. Compared with CdS, CS-2 Exhibits 18 times higher visible-light H 2 evolution activity using lactic acid as sacrificial agent and shows 7.8-fold higher photocurrent density. Moreover, photoelectrochemical test manifests the efficient separation of the photo-induced charge carriers. Radical-trapping experiments along with in-situ Pt photodeposition further prove that the charge transfer and separation follows Z-scheme mechanism. This work highlights the critical role of defects in the formation of direct Z-scheme composite. [ABSTRACT FROM AUTHOR]

Highlights: [•] W18O49/TiO2 hybrid achieves significant synergetic promotion on the photoactivity and photostability. [•] W18O49(10wt%)/TiO2 and W18O49(90wt%)/TiO2 show 2.43 (2.64) and 1.31 (1.52) times higher activity than the calculated baseline in degradation of MO (phenol), under UV–vis and visible light, respectively. [•] Well-matched band structure between W18O49 and TiO2 enhances the photo-induced charge separation and transfer. [•] ·O2 − and hole, especially the former, are the active species involved in the photodegradation. [ABSTRACT FROM AUTHOR]

• All-in-one Pt·Ni(OH) 2 /C 3 N 4 photocatalyst realizes one-step overall water splitting. • Pt·Ni(OH) 2 /C 3 N 4 achieves a prominent AQE of 4.2% at 420 nm and excellent stability. • Both H 2 O activation and charge transfer are dramatically enhanced. • The backward recombination of H 2 and O 2 is suppressed. Overall water splitting is vital in solar-hydrogen conversion. In addition to charge separation, the regulation of surface kinetics and suppression of backward reaction become particularly crucial. Herein, an all-in-one Pt·Ni(OH) 2 /C 3 N 4 photocatalyst is proposed by integrating Pt@Ni(OH) 2 composited nanowires and isolated Pt clusters on C 3 N 4. In this heterostructure, Pt@Ni(OH) 2 with rich coordinatively unsaturated sites effectively boost O 2 evolution, and Pt-O-Ni interaction retards O O bond cleavage thus inhibiting backward H 2 O regeneration. Meanwhile isolated Pt forms an Schottky junction with C 3 N 4 for electron transfer and proton reduction. Consequently, Pt·Ni(OH) 2 /C 3 N 4 achieves stoichiometric water splitting with H 2 /O 2 evolution of 1330/632 μmol g−1 h−1, and an outperforming AQE of 4.2% at 420 nm. Our work manifests that accelerating charge migration, inhibiting backward reaction and tuning surface kinetics are dominant in water splitting, for which a rational design of robust redox pathways is necessary. [ABSTRACT FROM AUTHOR]