In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co ²⁺

TLDR

Solar energy storage at scale requires efficient conversion of sunlight into chemical energy, and natural photosynthesis achieves this by splitting water into oxygen and hydrogen equivalents. This study aims to develop an artificial water‑splitting catalyst that generates oxygen from water without excessive driving potentials. The catalyst is generated in situ by oxidatively polarizing an inert indium tin oxide electrode in phosphate‑buffered water containing Co²⁺ ions. Analytical evidence shows a 1:2 phosphate‑to‑cobalt ratio, the pH dependence indicates hydrogen phosphate as the proton acceptor, and the catalyst, formed from earth‑abundant materials, operates in neutral water under ambient conditions.

Abstract

The utilization of solar energy on a large scale requires its storage. In natural photosynthesis, energy from sunlight is used to rearrange the bonds of water to oxygen and hydrogen equivalents. The realization of artificial systems that perform "water splitting" requires catalysts that produce oxygen from water without the need for excessive driving potentials. Here we report such a catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water containing cobalt (II) ions. A variety of analytical techniques indicates the presence of phosphate in an approximate 1:2 ratio with cobalt in this material. The pH dependence of the catalytic activity also implicates the hydrogen phosphate ion as the proton acceptor in the oxygen-producing reaction. This catalyst not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.