Micropores regulating enables advanced carbon sphere catalyst for Zn-air batteries

Energy conversion technologies like fuel cells and metal-air batteries require oxygen reduction reaction(ORR)electrocatalysts with low cost and high catalytic activity.Herein,N-doped carbon spheres(N-CS)with rich micropore structure have been synthesized by a facile two-step method,which includes the polymerization of pyrrole and formaldehyde and followed by a facile pyrolysis process.During the preparation,zinc chloride(ZnCl2)was utilized as a catalyst to promote polymerization and provide a hypersaline environment.In addition,the morphology,defect content and activity area of the resultant N-CS catalysts could be regulated by controlling the content of ZnCl2.The optimum N-CS-1 catalyst demonstrated much better catalytic activity and durability towards ORR in alkaline conditions than commercial 20 wt%Pt/C catalysts,of which the half-wave potential reached 0.844 V vs.RHE.When applied in the Zn-air batteries as cathode catalysts,N-CS-1 showed a maximum power density of 175 mW cm^(-2) and long-term discharging stability of over 150 h at 10 mA cm^(-2),which outperformed 20 wt%Pt/C.The excellent performance could be due to its ultrahigh specific surface area of 1757 m2 g
1 and rich micropore channels structure.Meanwhile,this work provides an efficient method to synthesize an ultrahigh surface porous carbon material,especially for catalyst application.

Boride-based electrocatalysts:Emerging candidates for water splitting

Electrocatalytic water splitting(EWS)is a promising route to produce hydrogen in a sustainable and environment-benign manner.To realize the large-scale hydrogen production,it is paramount to develop desirable electrocatalysts with engineered structure,high catalytic activity,facile accessibility,low cost,and good durability.Of late,boride-based materials,especially transition-metal borides(TMBs),are emerging as promising candidates for the EWS process.However,so far,ittle attempt has been made to provide a comprehensive summary on these findings.Herein,this review provides the up-to-date status on upgrading the catalytic performance of TMB-based nanomaterials by regulating the internal and external characteristics.The conventional synthetic techniques are first presented for the preparation of TMB-based catalysts.Afterwards,the advanced strategies are summarized to enhance the catalytic performance of TMBs,including morphology control,component regulation,phase engineering,surface oxidation and hybridization.Then,the design principles of TMB-based electrocatalysts for high-performance EWS are outined.Lastly,the current challenges and future directions in the development of TMB-based materials are proposed.This review article is expected to envisage insights into the TMBs-based water splitting and to provide strategies for design of the next-generation TMB-based electrocatalysts.