Rational Design of Spinel Cobalt Vanadate Oxide Co₂ VO₄ for Superior Electrocatalysis.

Abstract

Electrochemical energy devices, such as fuel cells and metal-air batteries, convert chemical energy directly into electricity without adverse environmental impact. Attractive alternatives to expensive noble metals used in these renewable energy technologies are earth-abundant transition metal oxides. However, they are often limited by catalytic and conductive capabilities. Here reported is a spinel oxide, Co₂ VO₄ , by marrying metallic vanadium atomic chains with electroactive cobalt cations for superior oxygen reduction reaction (ORR)-a key process for fuel cells, metal-air batteries, etc. The experimental and simulated electron energy-loss spectroscopy analyses reveal that Co²⁺ cations at the octahedral sites take the low spin state with one e_g electron <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>(</mo> <msubsup><mi>t</mi> <mrow><mn>2</mn> <mi>g</mi></mrow> <mn>6</mn></msubsup> <msubsup><mi>e</mi> <mi>g</mi> <mn>1</mn></msubsup> <mo>)</mo></mrow> </math> , favoring advantageous ORR energetics. Measurement of actual electrical conductivity confirms that Co₂ VO₄ has several orders of magnitude increase when compared with benchmark cobalt oxides. As a result, a zinc-air battery with new spinel cobalt vanadate oxide as the ORR catalyst shows excellent performance, together with a record-high discharge peak power density of 380 mW cm^-2 . Crucially, this is superior to state-of-the-art Pt/C-based device and is greatest among zinc-air batteries assembled with metal, metal oxide, and carbon catalysts. The findings present a new design strategy for highly active and conductive oxide materials for a wide range of electrocatalytic applications, including ORR, oxygen evolution, and hydrogen evolution reactions.