Preparation And Investigation Of Biomass-derived Carbon-based Non-precious Metal Electrocatalysts

The key of clean and high-efficiency energy conversion and storage technologies,such as fuel cells,water decomposition and metal-air batteries,are anodic oxygen reduction reaction（ORR）,hydrogen evolution reaction（HER）and cathodic oxygen evolution reaction（OER）.Currently,platinum and its alloys are the most efficient electrocatalyst for the ORR and HER,whereas iridium and ruthenium oxides（Ir O₂and Ru O₂）are highly active electrocatalysts towards the OER.However,the main drawback hampers their widely practical applications in energy storage and energy conversion technologies by limited reserves,high cost and poor stability of precious metals.Additionally,it is difficult for these precious metals to show satisfactory ORR,HER and OER activities.To achieve the prospect of commercial applications of energy conversion and storage technologies,exploring advanced and inexpensive non-precious metal electrocatalysts for ORR,HER and OER to replace precious metal catalysts is highly crucial.Among numerous non-precious metal electrocatalysts,the synergistic interaction between non-precious metal and N-doped carbon matrix can effectively modify the local electronic structure,thus optimizing the intermediate adsorption and making it comparable to the activity of precious metal catalysts.Additionaly,the doping of coordination atoms（e.g.,N,S,P,O,F,B,etc.）and the optimal microstructure（e.g.,porous structure）are conducive to improving catalytic performance.Biomass is a widely distributed carbon source,which has the advantages of abundent microstructure,low-cost,renewable,environmentally friendly and wide source,and also possess a large number of heteroatoms（such as N,S,P,etc.）.It has been widely used as an ideal carbon carrier material in the field of catalysis.In this study,biomass with rich microstructure is used as carbon carrier,the composition and morphology of biomass carbon carrier are designed and regulated through a series of treatment methods.Then,non-noble metal and heteroatoms were introduced to prepare multifunctional electrocatalysts,which were applied to actual applications.The results of the study are mainly includes as follows:（1）Corn stalk soot（CSS）was selected as the carbon carrier,CSS and Fe-2,2′-bipyridine coordinated.Meanwhile,N atoms were introduced by adding melamine,and the pyrolysis Fe,N double doped porous carbon nanosheets（Fe-MNC）catalysts were prepared.A series of control experiments were performed to deeply study the optimal structure and composition of the catalysts.The structure and properties of the catalysts were systematically studied by comparing with samples without addition of melamine（Fe-NC）,without addition of 2,2’-bipyridine（Fe-MC）,the pyrolysis mixture of melamine and CSS（MC）and pyrolysis pure melamine（PMel）.The experimental results indicate that the SEM images of Fe-MNC shows thinner and more wrinkled nanoflakes compared with interconnected spherical CSS and Fe-NC.In alkaline medium,the onset potential of Fe-MNC for ORR is as high as 0.99 V（vs.RHE）and the half-wave potential is0.85 V（vs.RHE）,which is comparable to the performance of commercial Pt/C.At the current density of 10 m A cm^-2,the OER（309 m V）overpotential of Fe-MNC was 39 m V lower than that of commercial Ru O₂（348 m V）.A rechargeable zinc-air battery was assembled by using Fe-MNC as the cathode of the zinc-air battery,with a specific capacity of 767.4 m Ah g^-1and a power density of 137 m W cm^-2at10 m A cm^-2.（2）Lotus fiber（LF）was selected as carbon carrier,and N/S-codoped lotus fiber（NSC）as a carbon base to support electrocatalytic Co₉S₈nanoparticles.Meanwhile,the composition and structure of the material were studied in depth,and its influence on the electrocatalytic performance is included,which was applied to practical applications.The SEM images of Co₉S₈-NSC show that Co₉S₈were implanted in the NSC matrix indeed.The size of Co₉S₈nanoparticles in NSC was smaller and more uniform compared with pure Co₉S₈nanoparticles.At the current density of 10 m A cm^-2,the HER overpotential and OER overpotential of Co₉S₈-NSC were 172 m V and 276 m V,which superior than other recently reported HER and OER catalysts.In alkaline medium,the ORR half-wave potential of Co₉S₈-NSC（0.87 V vs.RHE）was higher than commercial 20%Pt/C（0.833V vs.RHE）for 37 m V.Meanwhile,the stability of Co₉S₈-NSC was better than Pt/C and Ru O₂.Rechargeable zinc-air battery was assembled by using Co₉S₈-NSC as the cathode of zinc-air battery.The Co₉S₈-NSC Zn-air batteries could produce a larger specific capacity and energy density of 779.7 m Ah g^-1under discharge at j=10m A cm^-2.It proved that the Co₉S₈-NSC possess great potential as the oxygen electrode for rechargeable Zn-air batteries.