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Tungsten phosphide (WP) as an excellent hydrogen evolution reactions (HER) catalyst has attracted widespread attention, but its HER activity is low in alkaline media due to high water dissociation barrier. Herein, noble-metal-free cocatalyst WP/WO 3 composite was synthesized by adjusting the P/W molar ratio in the raw material using a simple solid phosphidation reaction. The structure, morphology, composition, and optoelectronic properties of the as-synthesized samples were characterized by XRD, SEM, TEM, XPS, UV–vis DRS, PL techniques, and electrochemical methods. Under visible light irradiation (λ ≥ 420 nm), the photocatalytic HER activities of the as-prepared samples using Eosin-Y (EY) dye as a sensitizer and trimethylamine (TMA) as an electron donor were investigated. The result shows that WP/WO 3 composite as a cocatalyst exhibits excellent photocatalytic HER activity and good stability. The highest apparent quantum yield (AQY) reaches 32.8 %. The presence of amorphous WO 3 in crystalline WP can improve the separation efficiency of photogenerated electrons and holes, reduce HER overpotential, and promote the dissociation of H 2 O in alkaline media. Therefore, the photocatalytic HER activity of WP/WO 3 composite is higher than that of single crystalline WP. [Display omitted] • WP/WO 3 composite was prepared by adjusting the P/W molar ratio in the raw material. • WP/WO 3 composite exhibits high dye-sensitized photocatalytic HER activity. • WO 3 coupling with WP promotes the separation of photocarriers and H 2 O dissociation. • The AQY of 32.8 % at 420 nm is achieved under the optimized conditions. [ABSTRACT FROM AUTHOR]

Nickel species were loaded on titanate nanotubes (TNT) as a hydrogen evolution cocatalyst by an impregnation–calcination method. Nickel chloride, nickel nitrate and nickel acetate were used as the precursors. More Ni 2+ ions intercalate into the interlayer of TNT when nickel chloride is used as the precursor. In the calcination process, the titanate transforms into anatase TiO 2 , and Ni 2+ ions are reduced and doped partly in TiO 2 and titanate. The Ni 2+ ions intercalated into TNT inner can promote the phase transformation, growth of metal Ni particles and the Ni 2+ doping. The formed Ni particles can be oxidized in air to form core/shell Ni@NiO structure. The Ni 2+ doping promotes the formation of oxygen defects and increases the conductivity of TNT. The photocatalytic activity of Eosin Y-sensitized nickel-modified TNT for hydrogen evolution was investigated. The TNT modified with nickel chloride exhibit higher activity, which can be attributed to the higher conductivity and more effective formation of Ni@NiO structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • CoP/g-C 3 N 4 hybrid photocatalyst was prepared in which CoP acts as a noble-metal-free HER cocatalyst. • CoP/g-C 3 N 4 composite exhibits high dye-sensitized photocatalytic HER activity and stability. • Photogenerated electrons can effectively transfer among EY, g-C 3 N 4 and CoP. • The AQY of 56.3% at 420 nm is achieved under the optimized conditions. In this paper, CoP/g-C 3 N 4 composite photocatalysts were prepared, in which CoP was used as a noble-metal-free cocatalyst. Using dye Eosin Y (EY) as the sensitizer and triethanolamine (TMA) as the electron donor, the performance of the photocatalytic H 2 evolution reaction (HER) under visible light (λ ≥ 420 nm) was investigated. When the loading of CoP is 5 wt%, the CoP(5 wt%)/g-C 3 N 4 composite shows the best photocatalytic HER performance, even better than that of Pt(5 wt%)/g-C 3 N 4. The apparent quantum yield (AQY) achieves 56.3% under 420 nm light irradiation, one of the best values reported for noble-metal-free cocatalysts in the dye-sensitized HER system, and the catalyst also exhibits good stability under 36 h of irradiation. The high activity and stability of CoP(5 wt%)/g-C 3 N 4 are the results of efficient electron transfer among photoexcited EY, g-C 3 N 4 and CoP, and the excellent HER activity of CoP. [ABSTRACT FROM AUTHOR]

• Co(OH) 2 nanosheets with tiny Co nanocrystallines on RGO are transformed from large-particle CoO@Co/RGO in dye-sensitized photocatalytic reaction. • The formed Co(OH) 2 nanosheets on RGO surface act as the effective adsorption of OH– to promote water dissociation. • The exposed tiny Co nanocrystallines on Co(OH) 2 nanosheets provide sufficient adsorption sites for H*. • Co/Co(OH) 2 /RGO cocatalyst shows much improved photocatalytic HER activity than pristine CoO@Co/RGO. It is of huge challenge to develop stable and efficient non-metal based cocatalysts for photocatalytic hydrogen evolution reaction (HER) via dye sensitization. Herein, we demonstrate a composite featuring Co(OH) 2 nanosheets embedded with metal Co nanocrystallines on reduced graphene oxide (Co/Co(OH) 2 /RGO) as a durable cocatalyst, which is obtained from the CoO@Co/RGO composite in dye-sensitized photocatalytic HER process via the dissolution-precipitation reaction of Co element. The large CoO@Co nanoparticles (∼43 nm in diameter) are converted to thin Co(OH) 2 nanosheets, and tiny Co nanocrystalllines are exposed on the surface. As a fresh cocatalyst, Co/Co(OH) 2 /RGO is endowed with favorable adsorption sites of both hydrogen and hydroxyl. Such a phase and structure transformation leads to the high photocatalytic activity (136.1 μmol) of Co/Co(OH) 2 /RGO cocatalyst via dye sensitization, which is 3.7 times as much as that of pristine CoO@Co/RGO (36.7 μmol). The improved HER performance should be highly related to the more effective interfacial electron transfer ability, as reflected by transient absorption decays, and photocurrent test. Moreover, the Co/Co(OH) 2 /RGO cocatalyst shows a remarkable stability of photocatalytic H 2 evolution, as well as the structural and phase stability. This work provides a novel route to develop highly dispersive and efficient non-noble metal based cocatalysts, and a new vision to understand the dynamic structure–activity relationship of the cocatalysts. [ABSTRACT FROM AUTHOR]

• Nickel oxide/nickel carbide/graphene composite was synthesized via one-step thermal treatment. • The graphene increases the conductivity and the distribution of nickel species. • The nickel carbide acts as the active sites for hydrogen evolution reaction (HER). • The NiO improves H 2 O dissociation and HER in the basic solution. • The composite exhibits synergistic electrocatalytic and photocatalytic HER activity. To resolve the energy crisis and environment pollution, it is urgent to explore highly efficient and inexpensive catalysts for hydrogen evolution reaction (HER). In this work, we fabricate nickel oxide/nickel carbide/graphene (labeled as NNG) composite via one-step thermal treatment of NiCl 2 /graphene oxide (GO) as the precursor at relatively low temperature. GO plays a role of the carbon source to form nickel carbide and increases the distribution of the nickel species. The formed nickel carbide acts as the active sites for hydrogen atoms adsorption (H ads). The NiO contacted with the nickel carbide promotes the Volmer reaction: H 2 O+e → H ads +O H -. The two different adsorption sites (nickel carbide for H ads , NiO for OH−) jointly lead to the HER synergistic effect in basic solution. The obtained composites exhibit much higher dye-sensitized photocatalytic and electrocatalytic HER activities than nickel carbide, NiO and RGO alone. The highest apparent quantum yield (AQY) of dye-sensitized hydrogen evolution for NNG12 at 420 nm reaches 39.4%. And the electrocatalytic HER overpotential is -0.28 V at the current density of 10 mA cm-2 in 1.0 mol L-1 KOH. To the best of our knowledge, it is the first time to report nickel oxide/nickel carbide as an efficient HER catalyst in alkaline media. This work paves a way for facile and green fabrication of the efficient HER cocatalysts. [ABSTRACT FROM AUTHOR]

The reasonable introduction of Cu into Ni significantly enhances the metal-support interaction of NiCu/graphene cocatalysts, which gives rise to smaller size of NiCu nanocatalysts and facilitates the interface electron transfer for enhancing dye-sensitized photocatalytic H 2 evolution performance. [Display omitted] • The introduction of Cu enhances the metal-support interaction (MSI) between Ni and graphene. • The enhanced MSI facilitates the electron transfer from dye EY to NiCu/graphene cocatalysts. • The introduction of Cu modulates the hydrogen adsorption on NiCu alloy surface. • The electrocatalytic and dye-sensitized photocatalytic HER performances of NiCu/graphene cocatalysts are much improved. The modulation of metal-support interaction (MSI) is of particular interest in improving the catalytic performance of metal nanocatalysts. Herein, we adopt an alloying strategy to tune the MSI in graphene-supported Ni catalyst by introducing Cu. The NiCu/graphene cocatalysts (denoted as N x C y G) are facilely synthesized by directly calcinating the mixture of metal chlorides and graphene oxide for dye-sensitized photocatalytic hydrogen evolution reaction (HER). The results reveal the introduction of Cu significantly affects the MSI in N x C y G cocatalysts, and a reasonable Ni/Cu ratio (4:1) significantly enhances the MSI in N 4 C 1 G cocatalyst. Such an enhanced MSI facilitates the electron injection from excited dye to RGO and further transfer to the NiCu alloy, and leads to smaller size of NiCu alloy nanoparticles (NPs) with sufficient active sites. Moreover, the synergetic effect between Ni and Cu is conducive to optimize the hydrogen adsorption on NiCu surface. As a result, the N 4 C 1 G cocatalyst shows much improved electrocatalytic and photocatalytic HER performance compared with monometallic Ni/graphene and Cu/graphene. The apparent quantum yield (AQY) at 420 nm reaches up to 67.7 % in the dye-sensitization system. We believe that this work develops a facile and effective strategy to tune the MSI of metal/graphene catalysts for enhanced HER performance. [ABSTRACT FROM AUTHOR]