Recent progress in interfacial microenvironment regulation strategies on electrocatalytic conversion

In recent years, there has been significant progress in the development of efficient electrocatalytic system driven by renewable electricity. Beyond traditional electrocatalyst design, it has been demonstrated that the regulation of the local microenvironment at the electrode-electrolyte interface (within the nanoscale) has a profound impact on the electrocatalytic performance, with many significant progresses made in recent years. This article reviewed the recent progress in interfacial microenvironment regulation strategies on the electrocatalytic conversion (such as carbon dioxide reduction and biomass molecule conversion). Taking the development of the double layer structure theory as a main line, we first introduced each component of electric double layer (EDL) according to the Gouy-Chapman-Stern (GCS) theory, which is the most widely recognized theory. Based on the structure evolution of EDL and the interactions among the interfacial species, we categorized the microenvironment regulation strategies into four types, including interfacial electric field regulation, interfacial pH regulation, interfacial substrate concentration regulation, and interfacial species interaction regulation. Firstly, we described the fundamental characteristics of interfacial electric field and the associated potential of zero charge (PZC) parameters. We discussed the effects of electrolyte and additive cations on the interfacial electric field. Based on the existing adsorption models of interfacial water and cations, detailed discussions on the effects of the types and concentrations of cations on the reaction performance were presented. At the end, we pointed out that the surfactant cations have a unique impact on the reaction performance when they are adsorbed over electrode. Secondly, the discussion of interfacial pH regulation was given from two aspects: Cationic acidity regulation and interface pH enhancement. The former one emphasizes the stability of cations in interfacial pH changes, while the latter believes that the interfacial pH increased by cations would significantly enhance the selectivity of C2+ products in electrocatalytic CO2 reduction (CO2RR). In addition, the inhibition of hydrogen ion migration in acidic media was also widely reported. Thirdly, we discussed the impact of interfacial modification on substrate concentration enrichment. For CO2RR and organic substrate conversion reactions, we respectively introduced the effects of hydrophobic thiols and surfactant molecular modifications on reaction performance, with emphasis on their significant inhibition of side reactions through hydrophobic substrate enrichment. Fourthly, we pointed out the necessity of alkali metal cations for CO2RR according to several recent literatures with intriguing results. Subsequently, taking organic substrates with more complex structures as an example, the profound impact of alkali metal and surfactant cations and their interactions with substrates on reaction performance were discussed. Fifthly, we described a comprehensive application of the above interface control strategies in ionomer-involved systems in which the double layer structures are delicately modified. We first took anionic (such as Nafion) and cationic (such as poly (diallyl dimethylammonium chloride)) polymers as examples to introduce the effects of different types and ion densities of ionomer modifications on the electrocatalytic performance. Based on this understanding, we presented a rational design of composite structures with different types of ionomers in terms of physical and chemical structural assembly, providing an in-depth understanding of the structure-activity relationship of ionomer modification in regulating reaction performance. At the end of this review, we briefly discussed the relationship between the four regulation strategies presented in the article, summarized and discussed the current challenges on microenvironmental regulation, and envisaged a broad prospect of enzyme-like catalyst design for potentially regulating product stereoselectivity.