Role of rhodium doping into lanthanum cobalt oxide (LaCoO3) perovskite and the induced bifunctional activity of oxygen evolution and reduction reactions in alkaline medium

Abstract

Rhodium doping into the lanthanum cobalt oxide (LaCo 1-x Rh x O 3 ) has induced significant bifunctional electrochemical activity towards the OER and ORR in alkaline solution with a substantially lower OER/ORR onset potential of 1.36/0.73 V vs HRE, smaller Tafel slope (116/90 mV/dec), low charge-transfer resistance, and an OER and ORR potential gap of only 0.65 V. Transition metal oxides, especially perovskites, have been considered effective electrocatalysts for the oxygen evolution (OER) and oxygen reduction (ORR) reactions in an alkaline solution. Here, a series of lanthanum cobalt rhodium oxide perovskites with the chemical formula LaCo 1-x Rh x O 3 (LCRO, 0.1 ≤ x ≤ 0.70) were prepared through the approach of solid-phase synthesis and their bifunctional electrocatalytic activity was assessed for both the OER and ORR. The crystallinity, morphology, surface, and electrocatalytic features of the LCRO were significantly correlated with the rhodium content. The LaCo 0.7 Rh 0.3 O 3 electrocatalysts with x = 0.3 showed enhanced electrocatalytic bifunctional performance with a substantially lower OER/ORR onset potential of 1.38/0.73 V vs HRE, smaller Tafel slope (116/90 mV/dec), and low charge-transfer resistance, which is the most efficient catalyst among the other studied ratios and superior to the pristine lanthanum cobalt oxide benchmark electrocatalysts. The LaCo 0.7 Rh 0.3 O 3 electrode exhibit good bifunctional electrocatalytic behavior and long-term durability with an OER and ORR onset potential gap (ΔE = E OER − E ORR ) of only 0.65 V, which could be credited to the enriched oxygen vacancies, lattice expansion and the improved electrical conductivity upon the doping of larger size of Rh ions. The LaCo 1-x Rh x O 3 catalysts are obtained from abundant materials that have the potential of highly-active bifunctional OER and ORR electrocatalysts.