1 INTRODUCTION
As industrialization increases worldwide, the number of artificially generated greenhouse gases has risen, continuing to exacerbate climate change. [1-3] Efforts to reduce carbon dioxide (CO2), the primary contributor to this issue, are intensifying. Despite a temporary decline in global CO2emissions due to the COVID-19 pandemic in 2020, 2021 saw record-high carbon emissions of approximately 36.1 GtCO2, a 6.3% increase year-on-year.[4] The 2021 IPCC report states that the remaining carbon budget to limit anthropogenic warming to 1.5 °C and 2 °C above pre-industrial levels, starting from 2020, is 400 GtCO2 and 1,150 GtCO2, respectively.[5] Addressing climate change urgently requires innovative solutions.[6]
To meet this challenge, various technologies have been developed to convert CO2 into industrially useful chemicals, utilizing methods such as electrochemical reduction (ECR),[7-11] photochemical reduction (PCR),[12-15] and photoelectrochemical (PEC) reduction.[16] However, significant obstacles remain—CO2 molecules are thermodynamically stable and require considerable electrochemical overpotential for reduction. Besides, in aqueous electrolysis systems, the ECR of CO2competes with the hydrogen evolution reaction (HER), necessitating the suppression of the latter to enhance the catalytic activity of the CO2 reduction reaction (CO2RR). As depicted in Table 1, ECR involves a complex reaction mechanism, producing a range of hydrocarbon compounds and potential selectivity issues.[17,18] Product selectivity depends on the adsorption and activation energy of intermediates on the catalyst’s surface. For instance, HCOOH can be selectively produced through the formation of *OCHO, while *COOH is a key intermediate in the formation of CO.[19] The formed *COOH intermediate undergoes protonation to create a *CO intermediate, which then desorbs as CO. Besides HCOOH, the reaction mechanism for other hydrocarbon products involves the *CO intermediate.[18,19] Cu’s unique ability to support the formation of C2+ products via the two-electron reduction of CO2 is due to its distinctive properties: negative adsorption energy for the *CO intermediate and positive adsorption energy for the *H intermediate.[20] The *CO intermediate is pivotal in CO2 ECR, impacting C–C coupling reactions and opening pathways for C2+ product formation.[21]
Since the first PEC study achieved CO2 reduction using a p-GaAs photoelectrode in 1978, sustained efforts have been made to convert photo-driven CO2 into solar fuel across various fields.[22] PEC CO2RR has advantages over ECR, including utilizing the photovoltage generated by semiconductor photoelectrodes, reducing system complexity, and partially offsetting the electrical energy required for CO2reduction. Also, accelerated charge separation due to bias-induced band bending enables higher production rates than PCR. PEC cells typically comprise a photoactive semiconductor electrode (photoelectrode), an electrolyte, and a counter electrode with a metal electrode catalyst or a second photoelectrode. CO2 reduction occurs at the cathode, while water oxidation occurs at the anode, with the photoelectrode as either or both.[23-25]
In PEC, each electrode can optimize catalyst efficiency based on factors such as bandgap, surface energy, crystallinity, defect characteristics, and structural attributes. Interface engineering is a promising approach to overcoming the limitations observed in existing bulk materials. As illustrated in Figure 1A, this review is categorized into five sections: plasmonic noble metal cocatalysts, non-noble metal cocatalysts, junction engineering, nanostructure engineering, and defect engineering—from an interface perspective. These sections provide insights into recent research trends. We also aim to compare materials generated by PEC, categorizing them into C1 and C2+, and offer insights into future research directions. Through this article, we aspire to contribute to advancing PEC technology grounded in interface engineering, ultimately working toward achieving carbon neutrality.