Design Insights for Tuning the Electrocatalytic Activity of Perovskite Oxides for the Oxygen Evolution Reaction

Abstract

Rechargeable metal-air batteries and water electrolyzers based on aqueous alkaline electrolytes hold the potential to be sustainable solutions to address the challenge of storing large amounts of electrical energy generated from solar and wind resources. For these batteries and electrolyzers to be economically viable, it is essential to have efficient, durable and inexpensive electrocatalysts for the oxygen evolution reaction. In this manuscript, we describe new insights for predicting and tuning the activity of inexpensive transition metal oxides for designing efficient and inexpensive electrocatalysts. We have focused on understanding the factors determining the electrocatalytic activity for oxygen evolution in a strong alkaline medium. To this end, we have conducted a systematic investigation of nano-phase calcium-doped lanthanum cobalt manganese oxide, an example of a mixed metal oxide that can be tuned for its electrocatalytic activity by varying the transition metal composition. Using X-ray Absorption Spectroscopy (XANES), X-ray Photoelectron Spectroscopy (XPS), electrochemical polarization experiments, and analysis of mechanisms, we have identified the key determinants of electrocatalytic activity. We have found that the Tafel slopes are determined by the oxidation states and the bond energy of the surface intermediates of Mn-OH and Co-OH bonds while the catalytic activity increased with the average d-electron-occupancy of the σ* orbital of the M-OH bond. We anticipate that such understanding will be very useful in predicting the behavior of other transition metal oxide catalysts.

Synthesis of graphitic-N and amino-N in nitrogen-doped carbon via a solution plasma process and exploration of their synergic effect for advanced oxygen reduction reaction

“…13 Meanwhile, oxygen reduction reaction (ORR) at the cathode allows the reduction of oxygen to hydroxide ions in alkaline electrolyte with the electrons obtained from the electrochemical oxidation of the metal anode. [14][15] In fact, ORR at the cathode plays the most important part in overall performance including discharge rate and capacity of metal-air battery. The desired cathodic reaction which is often referred as direct 4 electron transfer can be written as follows: [16][17] …”

Bi-Functional Oxygen Electrodes - Challenges and Prospects

“…They not only serve to decompose peroxide during oxygen reduction, but are also catalytically active for the oxygen evolution reaction. [32][33] The best-studied perovskites (general formula ABO 3 ) are the cobaltates, nickelates and manganates, which contain the rare-earth elements (lanthanum and neodymium) in the A site of the perovskite. To improve the conductivity of these perovskites, the A site is often substituted partially with calcium, barium or strontium.…”

“…Mixed-metal perovskites of the type AA´(BB´)O 3 (e.g., La 0.6 Ca 0.4 Co 1−x Mn x O 3 ) present the opportunity to tune the activity for oxygen reduction and oxygen evolution by changing the composition of the metals. 32,34 The onset potential for oxygen reduction on perovskite-carbon composites is in the range of 0.0 to −0.1 V vs. the mercury/ mercuric oxide (MMO) electrode. 26 This range of potentials is 0.4 V negative to the standard reduction potential for the oxygen reduction reaction.…”

“…Typical oxygen evolution activity on perovskite catalysts is about 5 mA/mg at 750 mV vs. NHE. 32 Cobalt and nickel based materials are generally more active, while manganese tends to reduce oxygen evolution activity.…”

The Influence of Fe Substitution in Lanthanum Calcium Cobalt Oxide on the Oxygen Evolution Reaction in Alkaline Media

“…An example of this is lanthanum cobalt oxide (LaCoO 3 ), in which partial substitution of lanthanum (3+) by calcium (2+) results in cobalt with varied oxidation states (2+, 3+, 4+), increased electrical conductivity and generation of oxygen vacancies. Several substitutions causing varied electrochemical performances have been reported for LaCoO 3 , [13][14][15][16][17] using Ca or Sr in the A site and Mn, Fe, Ni, Cu, among others, in the B site. Molecular orbital principles showed that an optimized catalyst for OER in alkaline media can be a perovskite containing cobalt and iron as the transition metal ions.…”