Unseock Kang

Photosynthesis of formate from CO2 and water at 1% energy efficiency via copper iron oxide catalysis

Solar conversion of carbon dioxide and water to value-added chemicals remains a challenge. A number of solar-active catalysts have been reported, but they still suffer from low selectivity, poor energy efficiency, and instability, and fail to drive simultaneous water oxidation. Herein, we report CuFeO2 and CuO mixed p-type catalysts fabricated via widely employed electroplating of earth-abundant cupric and ferric ions followed by annealing under atmospheric air. The composite electrodes exhibited onset potentials at +0.9 V vs. RHE in CO2-purged bicarbonate solution and converted CO2 to formate with over 90% selectivity under simulated solar light (air mass 1.5, 100 mW cm−2). Wired CuFeO2/CuO photocathode and Pt anode couples produced formate for over 1 week at a solar-to-formate energy conversion efficiency of ∼1% (selectivity >90%) without any external bias while O2 was evolved from water. Isotopes and nuclear magnetic resonance analyses confirmed the simultaneous production of formate and O2 at the stand-alone couples.

A facile synthesis of CuFeO2 and CuO composite photocatalyst films for the production of liquid formate from CO2 and water over a month

The development of low-cost photocatalysts capable of selectively producing liquid chemicals from CO2 and water with efficiency and durability comparable to typical photosynthetic values remains a great challenge. Herein, we report a facile, environmentally benign synthesis of CuFeO2 and CuO binary films by 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. The formate production is confirmed by quantitative analysis of H13CO2− produced from 13CO2. A time-resolved photoluminescence study reveals the sub-nanosecond charge transfer in binary CuFeO2 and CuO films, wherein the aqueous CO2 is adsorbed. An as-synthesized photocatalyst film with a three dimensional, double layer configuration shows the continued production of formate for over 17 d. 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 d.