Interfacial Structure Engineering,Electrocatalytic Performance And Applications Of Multifunctional Electrocatalyst Cobalt Oxide/Mesoporous N-doped Graphene Hybrids

With rising concerns about energy shortages and environmental pollution,researchers have contributed to search for clean and renewable energy sources to alternate fossil fuels.The hydrogen evolution reaction?HER?,oxygen evolution reaction?OER?,and oxygen reduction reaction?ORR?are of vital importance in designing the clean energy device.Up to date,transition metal carbon composite materials are regarded as the most promising catalysts for bifunctional catalysts,owing to that transition-metal–nitrogen–carbon?M–N–C,M=Fe,Co,Ni,ect.?,especially the pyridinic-N-Co bonding was efficient active site for ORR and OER.Recently,research demonstrate that carbon composites can promote the HER catalytic activity.However,little research has been done to distinguish the nitrogen configurations which played a vital role in adjusting the hydrogen adsorption to the right position.Herein,we adopt a two-step route to prepare the hybrid catalyst CoO/r-NLG with high density of pyridine-N-Co bond,and the total nitrogen doping content is 7.49%,especially the content of pyridine nitrogen has increased by 30%,compared to the one-step hydrothermal method.At the same time,the presence of the graphene ensures that the CoONPs have excellent dispersibility,and the particle size distribution is narrow,and the average particle size is about 6 nm.What's more,the optimal sample CoO/r-NLG-270 exhibits excellent trifunctional catalytic activity,compared with the CoO/r-NG which is not obtained by the LI-PLI method.In 1 M KOH solutions,the catalyst CoO/r-NLG-270 shows a positive half-wave potential of0.89V?versus RHE?,higher than the CoO/r-NG?0.84 V?,and the kinetic current density of CoO/r-NLG-270 after BET normalization is twice that of CoO/r-NG.In addition,the overpotential of the CoO/r-NLG-270 catalyst in HER and OER at a current density of 10 mA cm^-2is 123 mV and 295 mV,respectively.The TOF is addoped to represent the intrinsic catalytic activity of HER,and the TOF of CoO/r-NLG-270 is 0.256 s^-1,higher than that of CoO/r-NG(0.062 s^-1).Besides,the OER intrinsic activity is expressed by the area specific activity,the area specific activity of CoO/r-NLG-270 is 3.1 times that of CoO/r-NG.More importantly,through theoretical calculations,we found that it is pyridinic-N-Co bonds rather than pyrrolic-N-Co which can facilitate the adsorption of protons with a decrease of the Gibbs free energy to promote the HER.This work provides a way for the development of multifunctional electrocatalysts of non-noble metals for the highly demanded electrochemical energy technologies.