[광/전기화학 셀] PV-PEC 인공광합성 모듈 개발 ACS 논문 표지 게재

Nanostructured Au Electrode with 100 h Stability for Solar-Driven Electrochemical Reduction of Carbon Dioxide to Carbon Monoxide

Hyojung Bae, Chaewon Seong, Vishal Burungale, Myeongheon Seol, Chul Oh Yoon, Soon Hyung Kang, Wan-Gil Jung, Bong-Joong Kim,* and Jun-Seok Ha*

ACS Paper Cover published

■ INTRODUCTION

Because of global warming, it is essential to develop sustainable technology and protect the environment. It would be very helpful to reduce or stop carbon dioxide (CO2) emission into the environment by transforming CO2 into renewable fuels.

Electrochemical (EC) CO2 conversion is a promising candidate for large-scale carbon management applications because it can operate with high reaction rates and goodefficiency under ambient conditions. A typical EC system includes two electrically biased electrodes; CO2 and protons are converted into products at the negatively charge cathode, and H2O is oxidized into O2 and protons at the positively charged anode. The total cell voltage required for CO2 reduction includes potentials for both anodic and cathodic processes (Ecell = Eanode - Ecathode). However, compared with water splitting, EC CO2 reduction often presents significant constraints and high voltage requirements for achieving satisfactory reaction rates. These overpotentials represent wasted energy that can lead to inefficiencies. The insufficient activity and stability both limit the commercialization of the EC CO2 reduction. Therefore, it is imperative to develop a functional EC electrode and cost-effective EC system that effectively catalyzes both half-reactions with low overpotentials and high selectivities.

For resolving the insufficient activity, using photovoltaic (PV) cells for external energy is a potential approach because PV can harvest abundant solar energy. This energy can be used as an external energy source for carrying out EC CO2 reduction. The PVs can reduce the voltage required for the EC cell. Solar-driven chemical production involves the use of PV panels, modules, or cells connected in series to an EC system. This requires optimization of the voltage and current to efficiently combine the PV and EC systems, which can make it difficult to obtain a desirable product with high efficiency. Therefore, research has been performed to achieve high catalytic performance and selectivity.

White et al. reported a PV-EC system consisting of a Si PV solar array coupled with In cathode-based EC cells. These cells used a bicarbonate catholyte for the conversion of CO2 to formate and formic acid. Kauffman et al. used a commercial 6V Si solar module to power a two-chamber EC reactor with a Au cathode and a Pt anode, which was able to produce >400L/(gAu·h) of CO with a selectivity of approximately 96%. EC reduction of CO2 to CO is generally more energy-efficient and kinetically favorable than direct reduction of CO2 to multicarbon products such as CH4, C2H4, CH3OH, and C2H5OH. Therefore, CO is an attractive product for EC CO2 reduction. There are efficient metal catalysts for CO2 reduction to CO, such as Au, Ag, WSe2, ZnO, and MoS2. Au thin films are effective for efficient CO2 reduction to CO at modest overpotentials and high selectivity in comparison to hydrogen evolution. Specifically, nanoporous Au (pAu) has been reported to have a Faradaic efficiency (FE) of 95.9% at an applied potential of -0.6 V vs RHE for 10 h. Thus, we chose a pAu nanostructure that produced CO with high selectivity because of its large surface area and large number of active sites. We fabricated an EC cell with a pAu electrode as a cathode and an IrO2 electrode as an anode. The pAu electrode was fabricated using an anodization-reduction process. This Au catalyst exhibited excellent performance, with a CO FE of 100% at -0.75 V vs RHE. Furthermore, by using the catalyst for both the cathode and anode, we demonstrated a solardriven configuration for a triple-junction Si solar cell as a power source with a solar-to-CO conversion efficiency (SCE) of 5.3% and stability for >100 h.

acsomega.1c06720

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