Enhancing hydrogen evolution and oxidation kinetics through oxygen insertion into nickel lattice

Nickel-based materials,including metallic Ni and Ni oxide,have been widely studied in the exploration of non-precious-metal hydrogen electrocatalysts,but neither pure Ni nor NiO is ideal for the hydrogen evolution reaction(HER)and hydrogen oxidation reaction(HOR).In this paper,an oxygen insertion strategy was applied on nickel to regulate its hydrogen electrocatalytic performance,and the oxygen-inserted nickel catalyst was successfully obtained with the assistance of tungsten dioxide support(denoted as O-Ni/WO_(2)).The partial insertion of oxygen in Ni maintains the face-centered cubic arrangement of Ni atoms,simultaneously expanding the lattice and increasing the lattice spacing.Consequently,the adsorption strength of^(*)H and^(*)OH on Ni is optimized,thus resulting in superior electrocatalytic performance of0-Ni/WO_(2)in alkaline HER/HOR.The Tafel slope of O-Ni/WO_(2)@NF for HER is 56 mV dec^(-1),and the kinetic current density of O-Ni/WO_(2)for HOR reaches 4.85 mA cm^(-2),which is ahead of most currently reported catalysts.Our proposed strategy of inserting an appropriate amount of anions into the metal lattice could provide more possibilities for the design of high-performance catalysts.

Regulating electronic structure of porous nickel nitride nanosheet arrays by cerium doping for energy-saving hydrogen production

Water electrolysis for energy-efficient H_(2)production coupled with hydrazine oxidation reaction(HzOR)is prevailing,while the sluggish electrocatalysts are strongly hindering its scalable application.Herein,we schemed a novel porous Ce-doped Ni3N nanosheet arrays grown on nickel foam(Ce-Ni3N/NF)as a remarkable bifunctional catalyst for both hydrogen evolution reaction and HzOR.Significantly,the overall hydrazine splitting system can achieve low cell voltages of 0.156 and 0.671 V at 10 and 400 mA·cm^(−2),and the system is remarkably stable to operate over 100 h continuous test at the high-current-density of 400 mA·cm^(−2).Various characterizations prove that the porous nanosheet arrays expose more active sites,and more excellent diffusion kinetics and lower charge-transfer resistance,therefore boosting catalytic performance.Furthermore,density functional theory calculation reveals that the incorporation of Ce can effectively optimize the free energy of hydrogen adsorption and promote intrinsic catalytic activity of Ni_(3)N.

Al2O3-TiO2/ZrO2-SiO2 based porous ceramics from particle-stabilized wet foam

The porous ceramics based on Al2O3-TiO2/ZrO2-SiO2 from particle-stabilized wet foam by direct foaming were discussed.The initial Al2O3-TiO2 suspension was prepared by adding TiO2 suspension to partially hydrophobized colloidal Al2O3 suspension with equimolar amount,to form Al2TiO5 on sintering.The secondary ZrO2-SiO2 suspension was prepared using the equimolar composition,and to obtain ZrSiO4,ZrTiO4,and mullite phases in the sintered samples,the secondary suspension was blended into the initial suspension at 0,10,20,30,and 50 vol％.The wet foam exhibited an air content up to 87％,Laplace pressure from 1.38 to 2.23 mPa,and higher adsorption free energy at the interface of approximately 5.8×108 to 7.5×108J resulting an outstanding foam stability of 87％.The final suspension was foamed,and the wet foam was sintered from 1400 to 1600 ℃ for 1 h.The porous ceramics with pore size from 150 to 400 μm on average were obtained.The phase identification was accomplished using X-ray diffraction (XRD),differential thermal analysis (DTA),and thermogravimetric analysis (TGA),and microstructural analysis was performed using field emission scanning electron microscopy (FESEM).