Non-noble-metal biochars derived from biowastes for oxygen reduction reaction in fuel cell

Abstract

Fuel cell is a device converting the chemical energy into electricity through an electrochemical reaction At the cathode the hydrogen ions electrons and oxygen are reacted and produced water Compared to fossil fuels the fuel cell only produce electricity and water without the emission of pollutants so the fuel cell meets the concepts of environmental friendliness and clean energy However the sluggish kinetics of the cathodic oxygen reduction reaction and the high cost poor durability of noble metal catalysts limit the large-scale commercial applications In this study we recover lignocellulose biomass to synthesize non-noble metal catalysts and choose transition metal and potassium hydroxide as catalysts and activation agents respectively The samples after carbonization are activated by 800 W microwave radiation for 10 min The obtained biochars are washed with 0 5 M HCl to remove K ions For nitrogen doping a post-treatment is performed by using microwave radiation with 800 W under NH3 atmosphere By microwave irradiation we produced core-shell structured M-N-C catalysts Compared with lignin cellulose-derived catalysts display superior ORR catalytic activity (Eonset=-0 05 V) due to more Fe-Nx active sites and mesopore structure which can promote mass transport Moreover FeCo alloys with ratio (Fe:Co = 1:1) samples not only show a comparable activity but also exhibit a better stability and maintain 73% of current density after 10000s of operation In terms of biomass waste (sugarcane) the catalysts synthesized by Fe/Co (1:1) encapsulated with N doped carbon layers show a type IV adsorption-desorption isotherm indicating the existence of mesopores The formation of core-shell structure of FeCo alloys can be observed as evidenced by TEM Meanwhile the SC-Fe5Co5 exhibits excellent ORR catalytic activity (Eonset up to ?0 06 V) through four-electron pathways (n≒3 9) in the alkaline electrolyte and excellent resistance to methanol crossover Moreover the synthesis process via a microwave-assisted treatment could provide a facile and energy-effective route to construct core-shell structured metal-N-C

Date of Award	2019
Original language	English
Supervisor	Shou-Heng Liu (Supervisor)