Self-supported high-entropy alloy electrocatalyst for highly efficient H_(2) evolution in acid condition

Developing non-precious catalysts as Pt substitutes for electrochemical hydrogen evolution reaction(HER)with superior stability in acidic electrolyte is of critical importance for large-scale,low-cost hydrogen production from water.Herein,we report a CoCrFeNiAl high-entropy alloy(HEA)electrocatalyst with self-supported structure synthesized by mechanical alloying and spark plasma sintering(SPS)consolidation.The HEA after HF treatment and in situ electrochemical activation for 4000 cycles of cyclic voltammetry(HF-HEAa2)presents favourable activity with overpotential of 73 mV to reach a current density of 10 mA cm^(2) and a Tafel slope of 39.7 mV dec1.The alloy effect of Al/Cr with Co/Fe/Ni at atomic level,high-temperature crystallization,as well as consolidation by SPS endow CoCrFeNiAl HEA with high stability in 0.5 M H2SO4 solution.The superior performance of HF-HEAa2 is related with the presence of metal hydroxides/oxides groups on HEA.

Hydroxylated high-entropy alloy as highly efficient catalyst for electrochemical oxygen evolution reaction

Oxygen evolution reaction(OER),a half reaction involved in electrochemical water splitting,CO2 reduction,and metal–air batteries,restricts the efficiency of these energy conversion systems due to sluggish reaction kinetics[1,2].To accelerate OER,highly efficient electrocatalysts are required.However,large-scale applications of the normally used OER catalysts(i.e.RuO2 and IrO2)are hampered by their instability and low abundance.It is highly desirable to develop earth-abundant catalysts with low cost,high activity and long-term stability.Co(Ni,Fe)(oxy)hydroxides(Co(Ni)-(O)OH)have emerged as promising OER catalysts in recent years[3].

Reactive sintering of B4C-TaB2 ceramics via carbide boronizing:Reaction process, microstructure and mechanical properties

Carbide boronizing is a promising approach to obtain fine grained boron carbide based ceramics with improved mechanical properties. In this work, reaction process, microstructural characteristics and mechanical properties of BxC-TaB2(x = 3.7, 4.9, 7.1) ceramics were comprehensively investigated via this method. Dense BxC-TaB2 ceramics with refined microstructure were obtained from submicro tantalum carbide and boron powder mixtures at 1800℃/50 MPa/5 min by spark plasma sintering. The stoichiometry of boron carbide was determined from lattice parameters and Raman shift. It was found that uniformly distributed TaB2 grains in the BxC matrix is favor of the densification process and restricting grain growth.Besides, planar defects with high density were observed from the as-formed B7.1 C grains and transient stress was considered to contribute to the densification involved with plastic deformation. Microstructural observations indicate the dissolution of oxygen in the TaB2 lattice and most of the B7.1 C/TaB2 phase boundaries were clean. Owing to the highly faulted structure and finer grain size, as-obtained BxC-TaB2 ceramics exhibit high Vickers hardness(33.3–34.4 GPa at 9.8 N) and relatively high flexural strength ranging from 440 to 502 MPa.