Oxygen Sponges for Electrocatalysis: Oxygen Reduction/Evolution on Nonstoichiometric, Mixed Metal Oxides

Abstract

Electrocatalysis of oxygen reduction and evolution (ORR and OER) have become of significant importance due to their critical role in the performance of electrochemical energy conversion and storage devices, such as fuel cells, electrolyzers, and metal air batteries. While efficient ORR and OER have been reported using noble-metal based catalysts, their commercialization is cost prohibitive. In this Perspective, we discuss the potential of nonprecious metal based, mixed electronic–ionic conducting oxides (i.e., perovskites, double perovskites, and Ruddlesden–Popper (R-P) oxides) for efficient oxygen electrocatalysis at high and low temperatures. The nonstoichiometry of oxygen in these materials provides key catalytic properties that facilitate efficient ORR/OER electrocatalysis. We discuss the importance of surface structure and composition as critical parameters to understand and tune the ORR/OER activity of these oxides. We argue that techniques facilitating controlled synthesis and characterization of the surface structures are key at achieving a correlation between structure and activity of these materials. We make the case for combinatorial approaches involving quantum chemical calculations combined with detailed characterization, controlled synthesis, and testing as effective ways for developing the fundamental knowledge at the molecular level required to guide the design of efficient nonstoichiometric, mixed metal oxides for oxygen electrocatalysis. We conclude by summarizing current advances and devising future directions in this area.

Electrochemically Induced Phase Changes in La2CuO4 During Cathodic Electrocatalysis

“…The compositional tunability and capacity for oxygen non‐stoichiometry in Ruddlesden‐Popper oxides provide means to tune both ion and electron transfer behavior and optimize electrocatalytic properties for specific reactions . The combination of ionic conductivity and redox behavior that underpin the desired behavior, however, simultaneously introduces a risk of structural instability during catalytic operation.…”

“…Materials based on the perovskite crystal structure have maintained significant attention as electrocatalysts due to their amenability to compositional tuning . Ruddlesden Popper oxides (RPOs) are a class of perovskites that contain alternating layers of electrically insulating rock salt (AO) and semiconducting perovskite (ABO 3 ) crystal structures.…”

“…Ruddlesden Popper oxides (RPOs) are a class of perovskites that contain alternating layers of electrically insulating rock salt (AO) and semiconducting perovskite (ABO 3 ) crystal structures. This layered structure imparts numerous useful properties, including high ionic conductivity, the potential for superconductivity, and an ability to tolerate both interstitial oxygen and oxygen vacancies . The ability to accommodate both types of defect within the material has significant implications for electrocatalysis as it provides a synthetic avenue to tune the electronic properties of materials by tailoring oxygen non‐stoichiometry .…”

“…This layered structure imparts numerous useful properties, including high ionic conductivity, the potential for superconductivity, and an ability to tolerate both interstitial oxygen and oxygen vacancies . The ability to accommodate both types of defect within the material has significant implications for electrocatalysis as it provides a synthetic avenue to tune the electronic properties of materials by tailoring oxygen non‐stoichiometry . For example, oxygen vacancies have been shown to directly affect kinetics of both OER and ORR in these materials, and oxygen hyperstoichiometry influences catalytic activity by providing access to high valent oxidation states of transition metals within the lattice .…”

The effects of chemical treatment on the structural and thermal, physical, and mechanical and morphological properties of roselle fiber‐reinforced vinyl ester composites

“…a that the fibers contain impurities and wax, and there are many burrs on the fiber surface. Generally, the wax, impurities and other non‐cellulose constituents can be removed by alkalization which can improve their wettability.…”