As the tremendous use of fossil fuels, the atmospheric concentration of CO₂, which is recognized as green-house gas, has been gradually increased resulting that accelerates global warming and climate changes. To overcome these environmental problems, the huge efforts have been conducted to reduce and restrain the CO₂ emissions. The electrochemical CO₂ reduction (ECR) has recognized as one of the promising technologies that the CO₂ is electrochemically conversed to valuable fuels such as CO, HCOOH, CH₄, CH₃OH and C₂H₄. However, the ECR technology has the following several problems. First, the CO₂ molecule is thermodynamically stable that a large overpotential is required to split. Second, the various hydrocarbon compounds can be obtained following complex ECR mechanism, which results the product selectivity problems. Third, low solubility of CO₂ in aqueous electrolyte limits the mass transport to catalyst surface leading to the performance degradation. In addition, the hydrogen evolution reaction, recognized as a competing reaction, is more favorable than ECR in aqueous electrolyte systems. To overcome these problems, many researches have been conducted that improves the catalytic and systemic properties.

In catalytic part, understanding the catalytic properties is important that the product selectivity is related to binding energy of intermediates adsorbed on the catalyst surface. Accordingly, various studies have been investigated to improve the catalytic properties by modulating morphology, composition, crystal facet, grain boundary, and oxidation state. On the other hand, in addition to catalytic development, recent studies pay attention to improve the ECR systems. In the commercial ECR systems, current density of 200 mA cm^–2 is required to produce desire products with high selectivity. However, in conventional aqueous ECR systems, the only ~35 mA cm^–2 of current density is obtained due to the lack of CO₂ solubility in electrolyte. To overcome the limited CO₂ diffusion rate in aqueous electrolyte, recent studies has been focused to direct supply of gaseous CO₂ to catalyst. Furthermore, the introducing the membrane-electrode assembly (MEA) configuration to ECR systems has been investigated that minimizes the solution resistance and accelerates the formation of triple phase boundary at catalyst-membrane interfaces.

In this study, we investigate the MEA-type gas-phase CO₂ electrolysis system with anion exchange membrane. In addition, using electrodeposition method, the Zn-based electrocatalyst is fabricated onto porous gas diffusion layer, that produce the CO product from ECR. The fabricated Zn-based electrocatalyst is directly used to cathode of gas-phase ECR system and the humidified CO₂ gas is supplied into cathode resulting improvement of CO₂ mass transfer to catalyst-membrane interfaces. Compared to conventional aqueous ECR systems, further improvement of performance for CO production is demonstrated owing to minimized ohmic resistance and facilitated gaseous CO₂ utilization.