Highly efficient RuTe2/C electrocatalyst for oxygen reduction reaction in proton exchange membrane fuel cells

Abstract

It is desirable but challenging for ruthenium (Ru)-based chalcogenides to achieve high activity and good durability toward oxygen reduction reaction (ORR) in fuel cell applications. In this work, a facile microwave route followed by heat treatment was utilized to synthesize carbon supported ruthenium tellurium (RuTe2/C) catalysts, and the effects of heat treatment temperature on crystal structure, microstructure, chemical state, electrocatalytic activity, and fuel cell performance were studied. The mixed phase of predominant orthorhombic RuTe2 and minor hexagonal Ru was identified as dual active sites for RuTe2/C catalysts. Density functional theory calculations demonstrated that orthorhombic RuTe2 exhibits enhanced intrinsic activity relative to pure Ru due to the weakened absorption energies of oxygen intermediates. Because of the smallest nanoparticle size and complete formation of an orthorhombic RuTe2 structure, the best ORR performance was achieved with the RuTe2/C catalyst heat treated at 400 °C, showing a maximum half-wave potential of 0.70 V and only a 70 mV drop (10.0% loss) after 6000 potential cycles. In a H2/O2 fuel cell test, the best-performed RuTe2/C catalyst delivered a maximum power density of 672 mW⋅cm−2 using a low cathode Ru loading of 0.18 mg·cm−2, which is the best performance ever achieved for the Ru-based catalysts. After 6000 cycles of rigorous accelerated degradation test, the cell performance decayed by 55.4% because of the migrations of Te and Ru from the cathode side to the anode side and the growth of the RuTe2/C nanoparticles.