(Invited) A Wired Photosynthesis of Formate from Aqueous CO2 Using Earth Abundant Catalysts

Abstract

Harnessing and utilizing sunlight at high efficiency have represented an enormous challenge to the achievement of a carbon neutral society over the past four decades. Photocatalysis uniquely mimics natural photosynthesis in terms of light absorption and conversion, as well as storage of the absorbed photon energy into chemical bond energy. Despite this similarity, the development of low cost photocatalysts capable of selectively producing liquid chemicals from CO2 and water with efficiency and durability comparable to those in typical photosynthesis remains a great challenge. Most of the photocatalyst suspension systems produce mixtures of gas and liquid products at poor efficiencies, whereas electrically biased film systems exhibit a near-commercial gas production efficiency, albeit only for disappointingly short periods. Herein, we report the facile, environmentally benign synthesis of CuFeO2 and CuO binary films via electrodeposition, and demonstrate that these binary films produce only liquid formate from aqueous CO2 at ~1% energy efficiency, while driving O2 evolution from water on a wired Pt plate under continuous irradiation of simulated sunlight (AM 1.5G; 100 mW×cm- 2) over 24 h. An as-synthesized photocatalyst film with a three-dimensional, double-layer configuration further shows the continued production of formate for over 17 days. However, the crystalline structure and elemental state of the used photocatalysts undergo gradual chemical reduction. Such a deformation can be thermally healed by recycling the weekly used samples via oxidative annealing. Thus, a single photocatalyst sample produces formate continuously for 35 days. The photocatalyst components (Cu, Fe, and O) are earth-abundant, and the photocatalyst synthesis is straightforward, facile, environmentally benign, reproducible, and scalable. On achieving higher efficiencies in the future, the practical applicability of these photocatalysts will become enormous.