Surface Design And Active Site Regulation Of 3d Transition Metal Hydroxide-based Electrocatalysts

3d metal hydroxide,especially the emerging ferric,cobalt,nickel hydroxide and their derivative material,has provided us a good opportunity to design and synthesis of low-cost,highly active and durable electrocatalysts.Hydroxide has been widely used as the support to immobilized noble metals for its controllable surface composition,surface charging as well as surface catalytically active centers.Furthermore,3d metal hydroxide derived phosphides electrocatalysts has shown excellent performance in catalytic conversion of small molecular into fuels.In this paper,a site-specific layered hydroxide has been prepared for the immobilization of noble metal nanocrystals,and the stability of the anchored noble metal catalyst was dramatically enhanced.Synergistically doped with dual-metal sites as well as the utilization of defects engineering toward hydroxide derived phosphides,endow the phosphide electrocatalyst with both high activity and long-term stability.Main research results are as follows:1.Atomic scale site-specific hydroxide surface has been prepared to immobilize Pt nanocrystals,thereby enhanced the durability of composite electrocatalysts during electrocatalytic methanol oxidation.Fe3+ was introduced to partly substitute Ni2+ in the host structure of Ni(OH)2 nanosheet,then the coordinatively unsaturated and positively charged Fe3+ sites can adsorb PtCl42-through the Columbian Force.Subsequently,photochemical method was utilized to reduce PtCl42-and direct promote the growth of highly dispersed Pt nanoparticles on nickel-ferric layered double hydroxide(at nanometer scale or sub-nanometer scale).Both experimental results and theoretical analysis confirmed that the Fe3+ centers,in the host structure of Ni(OH)2 nanosheet,can provide strong interfacial contact with Pt nanocrystal through Fe3+-O(H)-Pt bonds,therefore enhance the durability of anchored Pt nanocatalysts.2.Synergistically doped with dual-metal sites as well as the utilization of defects engineering toward hydroxide derived cobalt phosphides,endow the optimized cobalt phosphide nanocrystals with dramatically enhanced electrocatalytic performance in hydrogen evolution reaction.Both Mo6+ and Al3+ was introduced to partly substitute Co2+ in the host structure of Co(OH)2 nanosheets and formed a stable layered structure with edge-sharing MO6(M = Co,Al,Mo).Subsequently,CoMoAl hydroxide was in situ converted into Mo and Al co-doped CoP nanocrystals in a high temperature and PH3 atmosphere.Electrocatalytical hydrogen evolution tests showed that to drive 10 mA cm-2 current density in 1 M KOH solution and at a scan rate of 5 mv s-1,Mo and A1 co-doped CoP nanocatalyst only required 64 mV overpotential.Beyond that,the dynamic dissolution of Al species in CoMoAl-P catalyst exposed more catalytically active Co,Mo and P sites.Also,the Al-dissolved induced porousstructure further decreased the electrode/electrolyte interfacial impedance and accelerate the mass/electron transfer.As expected,the optimized Al-dissolved CoMoAl-P electrocatalyst only required 49 mV overpotential to obtain 10 mA cm-2 current density,in which the high activity is comparable to that of commercial Pt/C catalyst.