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Using urea oxidation reaction (UOR) instead of oxygen evolution reaction (OER) is one of promising strategies for significantly diminish power consumption for hydrogen production from electrochemical water splitting. The electrocatalysts with cost-effective, multifunctional and high-performance are urgently required for enhancing UOR and hydrogen evolution reaction (HER), but this remains a challenge. Herein, we designed a bifunctional Ni(OH) x /p-Ni catalyst by electrochemical oxidation of Ni(OH) 2 in-situ grown on the surface of porous Ni membrane (p-Ni) to generate more abundant high-valence Ni3+ active species, which is favorable for reducing the energy barrier of electrochemical reaction. At the same time, a large number of metallic oxygen bonds (Ni–O) were formed to optimize the reaction kinetics of the electrochemical process, thus promoting the overall urea electrolysis efficiency. In 1.0 M KOH with 0.3 M urea, the optimized Ni(OH) x /p-Ni only requires potentials of 1.38 V and 0.22 V to obtain a current density of 100 mA cm−2 for UOR and HER, respectively. Notably, by assembling the Ni(OH) x /p-Ni as the cathode and anode for hydrogen production from urea-assisted water splitting, it can drive a current density of 100 mA cm−2 at a low voltage of 1.52 V and has excellent stability. This work provides a feasible strategy for design efficiently non-noble metal electrocatalysts for energy-saving hydrogen production and purifying urea-rich wastewater. [Display omitted] • Nanoflowers Ni(OH) 2 /p-Ni was grown on porous Ni membrane by solvthremal oxidation. • Electrochemical oxidation in-situ generates abundant Ni3+ active species. • The Ni(OH) x /p-Ni exhibited excellent bifunctional performance for HER/UOR. • Replacing OER with UOR can significantly save energy for hydrogen production. [ABSTRACT FROM AUTHOR]

Designing highly active and durable catalysts is considered to be crucial for enhancing hydrogen evolution reaction (HER) from water electrolysis. Although some studies indicate that anatase TiO 2 is a promising candidate for electrolytic hydrogen evolution reaction, the influence of different crystalline phases of TiO 2 on the supported Ru catalysts for electrocatalytic HER performance is rarely systematically explored. Herein, a series of Ru/TiO 2 -X (X = R (Rutile), A (Anatase), and P25) catalysts were prepared to investigate the influence of the rutile and anatase phases of TiO 2 on the catalytic activity of Ru catalysts in HER. The findings demonstrate that the HER activity is much affected by the variation of the titania structure, when other factors are kept constant. The 15Ru/TiO 2 -R-H 2 has superior HER performance with a small overpotential of 63 mV to achieve a current density of 10 mA cm−2 in acidic electrolyte and 99 mV in alkaline electrolyte compared to 15Ru/TiO 2 -A-H 2 and 15Ru/TiO 2 -P25-H 2. This might be attributed to the faster electron transfer and lower Fermi level caused by the oxygen vacancy (V O) and strong metal-support interaction (SMSI), along with the exposure of active sites afforded by the highly dispersed ruthenium nanoparticles on the rutile TiO 2. Our results indicate that the presence of rutile TiO 2 support alone is adequate to maintain Ru in its most active form and make it a more performing catalyst, compared to anatase titania and P25. • Ru is supported on different crystalline phase of TiO 2 for electrocatalytic HER. • Partial Ru is incorporated the lattice of TiO 2 -R with SMSI effect. • Highly dispersed Ru and rich V O promote electrocatalytic HER. • Electron transfer from V O and Ti to surface Ru is conducive to optimizing HER. [ABSTRACT FROM AUTHOR]

The CeO 2 , which were prepared by hard-template method, soft-template method, and precipitation method, were used as support to prepare Ni/CeO 2 catalysts (named as NCT, NCS, and NCP catalysts, respectively). The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET). Hydrogen temperature-programmed reduction (H 2 -TPR) was also used to study the reducibility of the support nickel precursors. Moreover, CO 2 catalytic hydrogenation methanation was used to investigate the catalytic properties of the prepared NCT, NCS, and NCP catalysts. H 2 -TPR and XRD results showed that the NiO can be reduced by H 2 to produce metal Ni species, and the surface oxygen species existing on the surface of the support CeO 2 can also be reduced by H 2 to form surface oxygen vacancies. Low-angle XRD, TEM, and BET results indicated that the NCT and NCS catalysts had developed mesoporous structure and high specific surface area of 104.7 m 2 g −1 and 53.6 m 2 g −1 , respectively. The NCT catalyst had the highest CO 2 methanation activity among the studied NCT, NCS, and NCP catalysts. The CO 2 conversion and CH 4 selectivity of the NCT catalyst can reach 91.1% and 100% at 360 °C and atmospheric pressure. The NCP catalyst, which had low specific surface area and low porosity, performed less CO 2 conversion and higher CH 4 selectivity than the NCT and NCS catalysts till 400 °C. [ABSTRACT FROM AUTHOR]