A High-Entropy Oxide as High-Activity Electrocatalyst for Water Oxidation

Abstract

High-entropy materials are an emerging pathway in the development of high-activity (electro)catalysts because of the inherent tunability and coexistence of multiple potential active sites, which may lead to earth-abundant catalyst materials for energy-efficient electrochemical energy storage. In this report, we identify how the multication composition in high-entropy perovskite oxides (HEO) contributes to high catalytic activity for the oxygen evolution reaction (OER), i.e., the key kinetically limiting half-reaction in several electrochemical energy conversion technologies, including green hydrogen generation. We compare the activity of the (001) facet of LaCr0.2Mn0.2Fe0.2Co0.2Ni0.2O3‑δ with the parent compounds (single B-site in the ABO3 perovskite). While the single B-site perovskites roughly follow the expected volcano-type activity trends, the HEO clearly outperforms all of its parent compounds with 17 to 680 times higher currents at a fixed overpotential. As all samples were grown as an epitaxial layer, our results indicate an intrinsic composition–function relationship, avoiding the effects of complex geometries or unknown surface composition. In-depth X-ray photoemission studies reveal a synergistic effect of simultaneous oxidation and reduction of different transition metal cations during the adsorption of reaction intermediates. The surprisingly high OER activity demonstrates that HEOs are a highly attractive, earth-abundant material class for high-activity OER electrocatalysts, possibly allowing the activity to be fine-tuned beyond the scaling limits of mono- or bimetallic oxides.

Deeper mechanistic insights into epitaxial nickelate electrocatalysts for the oxygen evolution reaction

“…5g ). 49 We speculated that this enhancement of electrocatalytic activity may be the result of the synergistic behavior of multiple cations, since the adsorption and binding of water molecules to the surface has been shown to induce an appreciable change in oxidation state of Cr, Co, and Ni simultaneously ( Fig. 5h ).…”

Challenges and opportunities in 2D high‐entropy alloy electrocatalysts for sustainable energy conversion

“…In addition, the 2D HEAs with unique electronic structures can increase the electrocatalytic activity of OER. 103 Studies have shown that hydroxides or (oxygen) hydroxides of bimetals, such as NiFe and CoFe, are highly active low-overpotential OER electrocatalysts. 104 For example, Nguyen et al reported a novel high-entropy glycolic acid (HEG), whose main components are Co, Cr, Fe, Mn, and Ni, which served as a new high-performance electrocatalyst for water oxidation.…”

“…The rich electronic effects generated by the coupling of multiple metal atoms in 2D HEAs enable to provide a variety of catalytic active sites, achieve near‐continuous intermediate adsorption energy, and improve the electron transport in the OER process. In addition, the 2D HEAs with unique electronic structures can increase the electrocatalytic activity of OER 103 …”

Combinatorial Sputter Synthesis of Single‐Phase La(XYZ)O3 ± σ Perovskite Thin‐Film Libraries: A New Platform for Materials Discovery

“…The B-sites can only be occupied by transition metals such as Co, Mn, Fe, Ni, and V. The respective A-site and B-site elements can substitute each other but cannot switch their sites. [6] Elemental combinations up to high-entropy perovskites [7,8] were reported to be performant for electrocatalytic water splitting. The increase in chemical complexity provides more opportunities to optimize the materials for target applications.…”