Metal-free Carbon Materials For Electrochemical Reduction Reactions

At present,the shortage of fossil fuels and serious pollution have brought troubles to our lives.It is urgent to find a new development direction.Electrochemistry has attracted numerous attention,in which electricity can be generated by renewable energy such as solar energy,wind energy and tidal energy.In addition,the reaction process is simple,easy to operate and non-pollution.The common electrochemistry reactions are oxygen reduction reaction,hydrogen evolution reaction,carbon dioxide reduction reaction and nitrogen reduction reaction.Metal-free carbon materials have high electrical conductivity,thermal conductivity and optical properties.The electrical properties of the surface can be controlled in a simple way.Therefore,the preparation of efficient electrochemical catalysts is the focus of this research.The main contents of this paper are as follows:(1)we report the use of functionalized lignin biomass as both carbon and dopant source for the direct synthesis of N and S dual-doped carbon sheet networks with abundant mesopores and high surface area.The resulting N and S-doped porous carbon exhibits good activity,long-term durability,and high selectivity for metal-free oxygen reduction electrocatalysis,approaching the performance of 20 wt%Pt/C,the state of the art ORR catalyst.Our method using natural biological resources thus offers a promising way to produce very promising noble metal-free ORR catalysts with potential application in alkaline fuel cells and metal-air batteries.(2)we report simple ultrasonication assisted synthesis of nitrogen and boron dual-doped graphene oxide(NB/GO)and demonstrate its application as an effective ORR catalyst realizing predominantly 4e-reduction of O2 to OH-in 0.1 M KOH.Enhanced ORR electrocatalysis of the dual B and N co-doped GO as opposed to GO singly doped with B or N arises from the synergistic interaction of the boron and nitrogen species.The content and configuration of both N and B dopants can be readily tailored by controlling the ultrasonic conditions,thereby permitting tuning of the ORR activity.Furthermore,the developed NB/GO metal-free catalyst exhibited very promising long-term durability and resistance to methanol poisoning compared to the state-of the art Pt/C catalyst.(3)we report metal-free electrocatalysis of aqueous N2 reduction to produce NH3 by using defective reduced graphene oxide(DrGO).Such nonmetallic and dopant-free catalyst converted N2 to NH3 at a high faradaic efficiency and NH3 formation rate in acidic electrolytes.Experiments combined with density functional theory calculations showed that the defect sites consisting of unsaturated carbon[single vacancy(SV),double vacancy(DV),and-COOH]in DrGO exhibit improved NH3 selectivity by binding N2 strongly instead of H.In addition to improved selectivity,the calculated free energies for N2 reduction reaction at DrGO-COOH and DrGO-DV sites suggest that the thermodynamic ovepotentials of these metal-free catalysts are at least comparable to those of reported efficient transition metal-based catalysts.