| Oxygen reduction reaction(ORR)in fuel cells,hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)in water electrolysis,are three core reactions of the two important clean energy conversion technologies,respectively.The kinetics of these reactions relies significantly on the electrocatalysts applied.Noble metalshave been widely used to reach the standards of commercial applications,such as platinum,ruthenium and iridium-based electrocatalysts.Though they have shown excellent catalytic activities,their limited reserves and high costs greatly hinders their large-scale commercialization.Therefore,the development of novel cost-effective,highly-efficient and highly-durable non-noble-metal electrocatalysts has beenan important research subject in the above sustainable energy fields.Transition-metal compounds are promising materials for replacement of noble metal electrocatalysts due to their high conductivity,satisfactory physical and chemical stability,simple synthesis conditions,easy modifications and low costs.Most importantly,most of them have high affinities for hydrogen and oxygen,thus have attracted many research interests.However,the relationships of catalysts’ structures and properties as well as some important factors influencing the performances of electrocatalysts haven’t been discussed thoroughly.Based on those,this dissertationsynthesized several electrocatalysts with distinct structures based on transition-metal compounds and discussed the origins of the satisfactory performances which achieved some progress.Besides,the synthesis methods and the structure of products are both of some universality which can be extended to many other fields.The contents mainly studied in the dissertation areas follows: Through facile grain nucleation and growth of titanium nitride(TiN)nanoparticles on simultaneously generated nitrogen-doped graphene(NG)sheets under ammonia annealing,a TiN/NG hybrid was developed as an efficient electrocatalyst for ORR.It showedsatisfactory catalytic performances with positive reaction potential and high current density in a nearly four-electron pathway.Furthermore,the hybrid showed better methanol tolerance and long-term durability than commercial Pt/C catalysts in alkaline media,which makes it a promising cathode component in fuel cells.Regular hollow polyhedral cobalt phosphide(CoP Hollow Polyhedrons)electrocatalysts were developed for HER and OER catalysis templated by Co-centered MOFs through facile oxidation and phosphorization calcinations.The surface depression and hollow structure gavethem rich poresandsignificant specific surface areaswhich would provide abundant catalytic active sites.They showed excellent electrocatalytic performances for both HER and OER in acidic and alkaline media,respectively,with low reaction overpotentials and Tafel slopes,high current densities and good durabilities after long-term operations,which were remarkably superior to those of particulate CoP(CoP Particles)and comparable to those of commercial noble-metal catalysts.Therefore they are very promising for commercial applications.Self-supported ferric phosphidespherical clusterson Ti foil(FeP/Ti)were developed via low-temperature phosphidation ofhydrothermal-synthesized FeOOH/Ti precursor.The FeP/Ti electrode had large specific surface area,high porosity and high conductivity which would provide high catalytic activities.They showed excellent electrocatalytic performances for HER in acidic media with low overpotentials,high exchange current density and good long-termdurability,close to the performances of commercial Pt/C catalysts.In addition,the binder-free preparation method for this self-supported HER electrode could be extended to many other fields. |
