Self-Reconstructed Spinel Surface Structure Enabling the Long-Term Stable Hydrogen Evolution Reaction/Oxygen Evolution Reaction Efficiency of FeCoNiRu High-Entropy Alloyed Electrocatalyst.

High catalytic efficiency and long-term stability are two main components for the performance assessment of an electrocatalyst. Previous attention has been paid more to efficiency other than stability. The present work is focused on the study of the stability processed on the FeCoNiRu high-entropy alloy (HEA) in correlation with its catalytic efficiency. This catalyst has demonstrated not only performing the simultaneous hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with high efficiency but also sustaining long-term stability upon HER and OER. The study reveals that the outstanding stability is attributed to the spinel oxide surface layer developed during evolution reactions. The spinel structure preserves the active sites that are inherited from the HEA's intrinsic structure. This work will provide an insightful direction/pathway for the design and manufacturing activities of other metallic electrocatalysts and a benchmark for the assessment of their efficiency-stability relationship.

Plasmon-induced hole-depletion layer on p-n heterojunction for highly efficient photoelectrochemical water splitting.

The photoelectrocatalytic (PEC) water splitting efficiency of semiconductor photoelectrodes is mainly limited by the effective separation and transfer of photogenerated charges. Zinc indium sulfide-cuprous oxide (ZnIn2S4-Cu2O) p-n heterojunction is constructed to enhance the PEC properties of ZnIn2S4. The nickel hydroxide iron oxide (NiFeOOH) layer on the surface of the heterojunction can be used as a hole depletion layer under the induction of plasmon resonance of the most surface silver (Ag) (the holes transferred from Cu2O valence band to NiFeOOH layer can be excited by Ag to produce hot electron consumption, which makes the last remaining hot holes participate in the water oxidation reaction) to further promote the carrier separation and transfer. The results exhibit that ZnIn2S4/Cu2O/NiFeOOH/Ag photoelectrode with dramatically enhanced photocurrent density of 1.22 mA/cm2 at 1.23 V versus the reversible hydrogen electrode (VRHE), which is 9.4 times higher than the pure ZnIn2S4. This work provides a promising concept to design photoelectrodes efficiently in PEC water splitting.

Copper phosphide decorated g-C3N4 catalysts for highly efficient photocatalytic H2 evolution.

Designing functional heterojunctions to enhance photocatalytic hydrogen evolution is still a key challenge in the field of efficient solar energy utilization. Copper phosphides become an ideal material to serve as the cocatalysts during photocatalytic hydrogen evolution by virtue of the lower prices. In this study, we synthesized graphitic carbon nitride (g-C3N4) based catalysts loaded with copper phosphide (Cu3P, Cu97P3), which exhibit superior performance in photocatalytic H2 evolution. Ultraviolet (UV)-visible spectroscopy illustrated that the absorption of light strengthened after the loading of copper phosphide, and the time-resolved transient photoluminescence (PL) spectra showed that the separation and transfer of the photoexcited carriers greatly improved. Moreover, both copper phosphide/g-C3N4 photocatalysts exhibited a relatively high H2 evolution rate: Cu3P/g-C3N4 (maximum 343 µmol h-1 g-1), Cu97P3/g-C3N4 (162.9 µmol h-1 g-1) while copper phosphide themself exhibit no photocatalytic activity. Thus, the copper phosphides (Cu3P, Cu97P3) work as a cocatalyst during photocatalytic H2 evolution. The cycling experiments illustrated that both copper phosphide/g-C3N4 photocatalysts perform excellent stability in the photocatalytic H2 evolution. It is worth noting that while the NaH2PO2 was heated in the tube furnace for phosphorization to obtain Cu3P, the excessive PH3 could pass through the solution of CuSO4 to obtain Cu97P3 at the same time, which significantly improved the utilization of PH3 and reduced the risk of toxicity. This work could provide new strategies to design photocatalysts decorated with copper phosphide for highly efficient visible-light-driven hydrogen evolution.

Defective ultra-thin two-dimensional g-C3N4 photocatalyst for enhanced photocatalytic H2 evolution activity.

The two-dimensional semiconductor photocatalytic material has excellent photocatalytic H2 evolution activity. In order to further improve the hydrogen production activity of g-C3N4, this study improved the preparation process of g-C3N4 and obtained a new photocatalyst (name H-CN) with a higher absorption range, larger specific surface area, and faster hydrogen production activity. Compared with the originally prepared g-C3N4, the H-CN absorption range has been improved, and the utilization of visible light has reached 650 nm. When the doping amount of Pt cocatalyst was 1.0 wt%, the H-CN demonstrates excellent photocatalytic hydrogen production activity, with a hydrogen production rate of 4.3 mmol h-1·g-1, which was 7.0 times higher than that pure 1.0 wt% Pt/g-C3N4. The fluorescence spectroscopy of H-CN showed better separation of carriers and longer lifetime. This study has guiding significance for the preparation of subsequent ultra-thin nanosheet photocatalysts and the establishment of high-efficiency photocatalytic systems.

CoNiO2 as a novel water oxidation cocatalyst to enhance PEC water splitting performance of BiVO4.

A strategy is proposed for modifying BiVO4 photoanode with CoNiO2 as a novel water oxidation cocatalyst to enhance PEC water splitting performance. The results show that CoNiO2 has the following functions: reducing photogenerated charge recombination centers; providing trapping sites to promote charge separation; improving the stability of the overall system; providing more active sites; and offering a lower overpotential. The BiVO4/CoNiO2 photoanode has a higher photocurrent density (1.16 mA cm-2 at 1.23 V vs. RHE), a lower onset potential (∼0.06 V vs. RHE), a larger IPCE (34.37%) and ABPE (0.163%), better stability and good rates of hydrogen evolution (0.0148 µmol cm-2 min-1) and oxygen evolution (0.0076 µmol cm-2 min-1). The strategy provides promising prospects for achieving efficient PEC water splitting performance using water oxidation cocatalysts.

Synthesis of layer-like Ni(OH)2 decorated ZnIn2S4 sub-microspheres with enhanced visible-light photocatalytic hydrogen production activity.

Novel layer-like Ni(OH)2 co-catalyst-decorated ZnIn2S4 microsphere photocatalysts were synthesized for the first time via a facile in situ deposition method to boost the photocatalytic H2-production performance. The physical and optical properties of the as-prepared Ni(OH)2-ZnIn2S4 composite samples were characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffusion reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and surface photovoltage spectroscopy (SPV). The results indicate that the photocatalytic H2 evolution activity of the ZnIn2S4 microspheres under visible light irradiation significantly enhances by introducing inexpensive Ni(OH)2 as a co-catalyst. The 5 mol% Ni(OH)2-ZnIn2S4 sample shows the highest H2-production rate of 8.35 mmol g-1 h-1, which is 18 times higher than that of pure ZnIn2S4. Moreover, photocatalytic activity of the Ni(OH)2-ZnIn2S4 sample remains stable even after 4 cycling photocatalytic experiments. In addition, a possible mechanism on the enhanced photocatalytic activity was proposed and verified by surface photovoltage spectroscopy.

Synthesis of novel CoOx decorated CeO2 hollow structures with an enhanced photocatalytic water oxidation performance under visible light irradiation.

Cobalt oxide decorated octahedral ceria hollow structures (CoOx/CeO2) with various contents of CoOx nanoparticles were prepared via a simple chemical impregnation method. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse-reflectance spectroscopy (DRS), surface photovoltage spectroscopy (SPV) and transient photovoltage spectroscopy (TPV). The photocatalytic oxygen evolution via water oxidation was investigated for the as-prepared CoOx/CeO2 nanocage composites. The photocatalytic results indicate that the CoOx/CeO2 nanocage composite with 1 mol% CoOx shows the highest photocatalytic activity. The excellent photocatalytic activity can be attributed to the improved visible-light absorption of CoOx/CeO2 composites and the efficient separation of excited electron-hole pairs between CoOx and CeO2, which can effectively enhance the lifetime of charge carriers in the CoOx-modified samples and then improve the oxygen evolution activity. Cobalt oxide is expected to be an excellent water oxidation co-catalyst for semiconductor photocatalysts.

Synthesis of novel AuPd nanoparticles decorated one-dimensional ZnO nanorod arrays with enhanced photoelectrochemical water splitting activity.

The vertically aligned one-dimensional (1D) ZnO nanorod arrays decorated with AuPd alloy nanoparticles have been synthesized with ZnO nanorod arrays as template via a mild hydrothermal method. In this work, the as-prepared AuPd/ZnO nanorod arrays demonstrated high light-harvesting efficiency. The microstructures, morphologies and chemical properties of the obtained AuPd/ZnO composite photocatalyst were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectroscopy (XPS). The photoelectrochemical (PEC) performances of as-obtained AuPd/ZnO nanorod arrays were examined, and the photocurrent density was up to 0.98mAcm(-2) at 0.787V versus Ag/AgCl, which was about 2.4 times higher than the pure ZnO sample. A possible photocatalytic mechanism of the AuPd/ZnO hybrid nanostructures under the simulated sunlight irradiation was proposed to guide further improvement of other desirable materials. According to the above experiment results, it can be clearly found that AuPd/ZnO composite nanorod arrays showed excellent PEC performance and had promising applications in the utilization of solar energy.

Facile synthesis of Ag@CeO2 core-shell plasmonic photocatalysts with enhanced visible-light photocatalytic performance.

Novel Ag@CeO2 core-shell nanostructures with well-controlled shape and shell thickness were successfully synthesized via a green and facile template-free approach in aqueous solution. As-prepared samples were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflection spectroscopy (DRS), electron spin resonance (ESR) and photoluminescence spectroscopy (PL). The structures with different core shapes and controllable shell thickness exhibited unique optical properties. It is found that the nanoscale Ag@CeO2 core-shell photocatalysts exhibit significantly enhanced photocatalytic activities in the O2 evolution and MB dye degradation compared to pure CeO2 nanoparticals. The enhancement in photocatalytic activities can be ascribed to the localized surface plasmon resonance (SPR) of Ag cores. Moreover, larger active interfacial areas and contact between metal/semiconductor in the core-shell structure facilitate transfer of charge carriers and prolong lifetime of photogenerated electron-hole pairs. It is expected that the Ag@CeO2 core-shell structure may have great potential in a wider range of light-harvesting applications.