Designed Synthesis Of Non-noble Metal-based Dual-Site Catalysts For Alkaline Hydrogen Evolution Reaction

Owing to the widespread consumption of fossil fuels,the energy crisis and environmental pollution are the greatest challenges our society is currently experiencing.Therefore,the development of sustainable and clean electrochemical energy conversion technologies is an essential step in addressing these challenges.Among the various available strategies,electrochemical hydrogen production has attracted great interest because hydrogen is environment-friendly,renewable and has a high energy density.The catalyst is an important factor to enhance the efficiency of hydrogen production in electrolytic water.Typically,noble metal platinum-based catalysts and titanium alloy hardware are required to maintain the stability of the electrolyzer in a robust acid environment.In contrast,low-cost metals（Ni/Co/Fe）can be used as hardware materials or catalysts in alkaline media,thus providing greater cost and application advantages.However,hydrogen evolution reaction（HER）in alkaline electrolytic water tends to show relatively sluggish kinetics compared to acidic solutions,which becomes a key constraint to the efficiency enhancement of electrolytic water.Therefore,the exploration and development of alkaline hydrogen precipitation catalysts with excellent performance and low cost has become a hot research topic.Molybdenum is earth-abundant,inexpensive and Mo-based catalysts such as MoS2 and Mo2C have excellent HER activity and are ideal candidates for substituting Pt-based catalysts.For alkaline HER,the reaction is generally divided into two steps,namely the hydrolysis step and the hydrogen coupling step,however,the established Mo-based catalysts are difficult to provide ideal active sites for both steps,which limits the reaction rate of HER.Based on this,this paper focuses on the design of non-noble metal-based dual-site catalysts via a heterogeneous elemental doping strategy.On the one hand,elemental doping can change the electronic structure of the original catalyst,and on the other hand,it may generate additional reactive sites to facilitate the alkaline hydrogen evolution process.（1）We developed a dual-cation doping strategy to improve the alkaline HER performance of MoS2 nanosheets.The designed Ni,Co co-doped MoS2 nanosheets can promote the tandem HER steps simultaneously,thus leading to a much enhanced catalytic activity in alkaline solution,the overpotential of the Ni,Co-MoS2,at a current density of 10mA/cm2,is at least 50 mV lower than those of the mono-doped samples.The synergistic effect arising from the dual-cation doping promotes the tandem HER reaction and provides an effective way to improve the catalytic performance of MoS2 materials in alkaline solutions.（2）We successfully constructed B and N co-doped carbon encapsulated Mo2C nanoparticle composites（Mo2C@BNC）.Structural analysis of the surface Mo2C nanoparticles is encapsulated by an ultrathin carbon shell（carbon layer<3）,a unique structure that prevents oxidation of the active metal during catalysis.Electrochemical tests exhibited an overpotential of 99 mV at 10 mA/cm2,a Tafel slope of 58.1 mV/dec and good stability for the Mo2C@BNC sample in alkaline environment.Theoretical calculations show that the introduction of B enables the hydrolysis step to proceed spontaneously,while the B and N co-modified C elements exhibit near-zero H adsorption Gibbs free energy（-0.085 eV）,with the dual action of B and C facilitating the HER.