Preparation And Electrocatalytic Performance Of Biomass Carbon Catalyst Based On Chloro Phyll

As a new generation of clean and renewable energy technologies,hydrogen fuel cell has attracted people’s attention for its high efficiency and environmental protection.At present,there are many factors hindering the development of hydrogen fuel cells,among which the performance of electrocatalysts is one of the most important,especially,the development of efficient and cheap electrocatalysts for oxygen evolution（OER）,oxygen reduction（ORR）and hydrogen evolution（HER）is still a huge challenge.The most effective catalysts at present are precious metals such as Pt（for ORR and HER）and Ru O₂（for OER）,however,their scarcity and high prices prevent their large-scale use.Therefore,the exploration for inexpensive non-precious metal based catalysts for water splitting,fuel cells and metal-air batteries is the key to the development of clean renewable energy sources.Here,inexpensive and resource-rich spinach and algae were selected as precursors.Chloroplast based M-N-C（M=Fe,Co）electrocatalyst was prepared by adding amorphous catalyst and carbonization process.The electrocatalytic performance of the as-prepared ORR and HER catalyst was discussed.The main contents and conclusions are as follows:Firstly,Fe-N-C catalyst with good performance was successfully prepared from spinach by extraction of chloroplast and heat quenching treatment.The Fe-N-C material was characterized by scanning electron microscopy（SEM）,X-ray powder diffraction（XRD）,transmission electron microscopy（TEM）and Raman spectroscopy（Raman）.It was found that the material has a porous structure with a specific surface area of 128 m²g^-1,and the content of Fe and N are 0.45 at.%and 3.32 at.%,respectively.As an electrocatalyst for ORR,the onset potential is 0.97 V,and the half-wave potential is 0.83 V.At 0.80 V,the current density is 3.9m A cm^-2,which exceeds that of commercial Pt/C catalyst(3.5 m A cm^-2).Additionally,it has good durability and methanol resistance.It is proved that the preparation of highly dispersed metal atom based catalysts by forging and burning chlorophyll precursor system is an effective way to improve the catalytic performance.Secondly,in order to simplify the preparation process of the catalyst,Fe-N-C catalyst was prepared directly from algae which contain abundant chlorophyll.Using spirulina as raw material,Fe-N-C catalyst was obtained by pre-oxidation and ionic exchange process,followed by heat-treatment process.Fe-N-C catalyst was characterized by SEM,TEM,XRD and Raman.The porous structure of the material was found to be0.34 at.%and 4.86 at.%,respectively.When used as ORR catalyst,Fe-N-C showed the onset potential and half-wave potential of Fe-N-C of0.97 V and 0.85 V,respectively.The limiting current density is 5.0 m A cm^-2.The slope of Tafel is 49.80 m V dec^-1,which is very close to that of Pt/C(39.4 m V s^-1)and Fe-N-C catalyst prepared from spinach.Therefore,the efficient ORR catalyst can be prepared directly from algae containing chloroplasts,which greatly simplifies the production process.Finally,Co-N-C catalysts based on chlorophyll were successfully prepared on the basis of Fe-N-C materials prepared above,and their electrocatalytic performances on HER and OER were explored.The composition and structure of the materials were characterized by SEM,XRD,TEM and Raman.When Co-N-C was used as HER catalyst,it had a small overpotential(η₁₀=112 m V)comparable to that of Pt/C in 0.5 M H₂SO₄medium.The slope of Tafel is 86.0 m V dec^-1,which is similar to Pt/C.When Co-N-C was used as a catalyst for OER,the onset potential was 1.53 V,the overpotential(η₁₀)was 359 m V to achieve the current density of 10.0 m A cm^-2,and the slope of Tafel was 125.2 m V dec^-1,indicating its significant OER activity.In this paper,the transition metal and nitrogen co-doped biomass carbon catalyst was successfully prepared by ion exchange,pyrolysis and other processes by using chlorophyll-rich biomass as the precursor.Thanks to the high dispersion of metal atoms in the material,the catalysts showed excellent electrocatalytic performance for ORR and HER.It is very important for the development of cheap and efficient electrocatalysts and the high value utilization of biomass.