Metal Organic Framework Derived Heterogeneous Materials For Efficient Multi-functional Electrocatalysis

Technologies for large-scale energy storage require multi-functional energy conversion and storage systems,including metal-air batteries,metal-CO2 batteries and water splitting.The development of multi-functional electrocatalysts is urgently needed to combat the current energy crisis that the world faced.Recently much effort has been devoted to design efficient and cost-effective electrocatalysts for CO2 reduction reaction(CO2RR),oxygen reduction reaction(ORR),oxygen evolution reactions(OER),and hydrogen evolution reactions(HER),but the development of single catalyst which can catalyze all the processes simultaneously and efficiently is still a great challenge and no reports are being published to the dateIn the present work,we report a simple strategy for designing highly efficient catalyst for both oxygen reduction(ORR)and oxygen evolution reactions(OER).The catalyst is derived from dicyandiamide modified ZIF-67 by subsequent pyrolysis under inert conditions.Co single atoms are well dispersed over the surface of entire carbon nano tubes network formed upon pyrolysis with well-defined morphology,high porosity and unique structural features.The prepared electrocatalyst has shown up remarkable performance for both ORR and OER.The bifunctional property of the material is best amongst the previously reported catalysts.The catalyst shows highly positive onset potential value of?0.99 V vs.reversible hydrogen electrode(RHE)higher than that of Pt/C for ORR and half wave potential value of 0.86 V vs.RHE,also more positive than Pt/C in alkaline medium with small Tafel slope as well and high selectivity for four electron reduction process.A lower overpotential for OER of 300 mV is observed for onset potential of 1.53 V vs.RHE.Smaller value of overvoltage(?E)0.78 V pronounces the excellency of material for bifunctional catalysisIn second project,we report a simple strategy for designing highly efficient catalyst capable of catalyzing all these processess,with excellent activity and stability under technological conditions.The catalyst integrates bimetallic alloy and single atoms,with N-doped CNTs acting as substrate.As a result,the first ever tetra-functional electrocatalyst utilizing synergetic effect of multiple active sites is reported for utilization in multi-model energy conversion and storage system.The prepared electrocatalyst has shown up remarkable performance for ORR,OER,HER and CO2RR.The catalyst exhibits more positive onset(0.98 V)and half wave potential(0.86 V)than Pt/C for ORR,extremely low overpotential(?10)of 250 mV for OER and thus the lowest ORR/OER potential gap of 0.62 V.In alkaline medium,the catalyst also shows excellent HER performance with ?10 of 49 mV,resulting in the smallest cell bias of 1.57 V for overall water splitting to date.An excellent CO2RR with FE of 99%is achieved in 0.5 M KHCO3 medium.In another work,a novel trifunctional Br doped and defect-enriched porous carbon framework(BrHT@CoNC)is designed,which shows excellent electrocatalytic activity for oxygen reduction reaction(ORR),oxygen evolution reaction(OER)as well as hydrogen evolution reaction(HER).Combination of extensive defects and Br-doping into porous carbon is simply achieved by pyrolysis of the surfactant,dimethyldioctadecylammonium bromide(DODAB)modified ZIF-67.The BrHT@CoNC composite shows great potential as an economical catalyst/electrode for both rechargeable Zn-air batteries and overall water splitting.The successful doping of Br atoms into the carbon framework introduces more defects and thus electronic redistributions,which lead to excellent activity for electrocatalytic oxygen reduction reaction(ORR),oxygen evolution reaction(OER)as well as hydrogen evolution reaction(HER).For ORR,the prepared catalyst exhibits more positive onset and half wave potential(by 40 mV and 80 mV respectively)than commercial Pt/C.Overpotential(?10)of only 254 mV and 77 mV is required for OER and HER respectively in alkaline medium.The rechargeable Zn-air battery was assembled by using the catalyst as air cathode,which showed an output power density of 165 mWcm-2.The promising results shown by novel electrocatalysts will open up new paves for the scientific community to explore and investigate such materials.Our work will encourage scientists to design more stellar electrocatalyst which could be revolutionary for future renewable energy technology.This work also provides avenue toward the exploration of cost effective heteroatom doped catalysts for efficient integration of three or more functions in one freestanding electrode.