Synthesis Of High-performance Oxygen Reduction Electrocatalysts Based On Biomass And Waste Activated Carbon

The rapid development of the social economy and the acceleration of industrialization have led to an increase in energy consumption.And the carbon emissions cause lots of issues such as climate change,which have attracted widespread attention.Based on the targets of“Carbon Peak and Carbon Neutrality”,the new requirements are put forward for the development of new energy technologies.Therefore,the hydrogen energy of“zero-carbon energy”has a great potential.One of the utilization methods of hydrogen energy is the hydrogen-oxygen fuel cell,which has been widely studied as a device with its high energy conversion efficiency.The cathode oxygen reduction reaction（ORR）rate is slow.Nowadays,Pt-based electrocatalyst was commonly used to accelerate the ORR process.But its high cost,scarce resources,and poor stability seriously hindered the development of fuel cells.Therefore,there is an urgent need to develop an ORR non-noble metal carbon-based electrocatalyst with environmentally friendly,inexpensive,and excellent electrocatalytic activity.In this paper,biomass and waste activated carbon with abundant resources and natural advantages were selected as precursors.Through a simple and green synthesis strategy,ORR carbon-based electrocatalysts co-doped with non-noble metals and nitrogen elements were prepared.The main research contents and conclusions could be concluded as the following aspects:（1）Edible fungus residue was used as waste biomass in the food industry.It created a natural pore structure during the growth of the biomass matrix and retained a large amount of protein hyphae.So,it was selected as the carbon and nitrogen precursor.Then“Fe-N/C”porous carbon material（SN-Fe-ZA）was synthesized by ammonium phosphate hydrothermal and pyrolysis with zinc chloride and iron trichloride activation.SN-Fe-ZA showed a honeycomb pore structure and its specific surface area was up to1646.4 m²·g^-1.The proportion of pyridine nitrogen and graphitic nitrogen was up to56.2%,which was conducive to construct more active sites.The electrochemical test results indicated that SN-Fe-ZA had the best ORR electrocatalytic activity with the half-wave potential of 0.820 vs.RHE.Also,the limiting current density is 4.71 m A·cm^-2,which was higher than commercial Pt/C(4.22 mA·cm^-2).Besides,it showed a more excellent electrochemical stability and stronger methanol-tolerant.（2）Duckweed,as a water restoration plant,could absorb nitrogen pollution in the waste water.The waste duckweed had a large yield and was rich in protein.Therefore,it was selected as the carbon and nitrogen precursor.we selected zinc chloride and basic magnesium carbonate as the dual activator,and ferric chloride as the iron source to synthesize the transition metals and nitrogen co-doped carbon-based catalysts with hierarchically porous structure（D-ZB-Fe）.Results showed that D-ZB-Fe had a high specific surface area(1342.91 m²·g^-1)and total pore volume(1.085 cm³·g^-1),in which the volume of micropores was 0.566 cm³·g^-1 and mesopores was 0.533 cm³·g^-1.The characterization results showed that D-ZB-Fe contains a specific Fe-N_x structure and the functional nitrogen form accounts for the highest proportion（72.9%）.In addition,the half-wave potential was 0.857 V vs.RHE and the limiting current density was 4.808m A·cm^-2,suggesting D-ZB-Fe was superior to commercial Pt/C.Moreover,D-ZB-Fe showed an excellent stability and remarkably methanol tolerance by the durability test.（3）The activated carbon was often used in wastewater treatment to absorb organic matter or heavy metals.Meanwhile,it caused a large amount of waste activated carbon which needed to be treated urgently.The waste activated carbon derived from the adsorption of oily wastewater by activated carbon was selected as the precursor.The bamboo shavings with pre-activated to prepare carbon material.Then the oil phase was mixed with activated carbon to simulate“waste activated carbon”.Based on the synthetic strategy of（2）,the urea was added as nitrogen source and ferric chloride was used as iron source to prepare high-performance Fe/N co-doped ORR carbon-based electrocatalyst（DC-6）.The physical structure showed that the addition of oil phase had a positive effect on the formation of pore structure and element retention.In addition,the electrocatalytic activity,the resistance to methanol,and cycle stability of DC-6 were comparable to commercial Pt/C.