Tuning Structures and Microenvironments of Cu-Based Catalysts for Sustainable CO₂ and CO Electroreduction

ConspectusThe carbon balance has been disrupted by the widespread use of fossil fuels and subsequent excessive emissions of carbon dioxide (CO2), which has become an increasingly critical environmental challenge for human society. The production and use of renewable energy sources and/or chemicals have been proposed as important strategies to reduce emissions, of which the electrochemical CO2 (or CO) reduction reaction (CO2RR/CORR) in the aqueous systems represents a promising approach.Benefitted by the capacity of manufacturing high-value-added products (e.g., ethylene, ethanol, formic acid, etc.) with a net-zero carbon emission, copper-based CO2RR/CORR powered by sustainable electricity is regarded as a potential candidate for carbon neutrality. However, the diversity of selectivities in copper-based systems poses a great challenge to the research in this field and sets a great obstacle for future industrialization.To date, scientists have revealed that the electrocatalyst design and preparation play a significant role in achieving efficient and selective CO2-to-chemical (or CO-to-chemical) conversion. Although substantial efforts have been dedicated to the catalyst preparation and corresponding electrosynthesis of sustainable chemicals from CO2/CO so far, most of them are still derived from empirical or random searches, which are relatively inefficient and cost-intensive. Most of the mechanism studies have suggested that both intrinsic properties (such as electron states) and extrinsic environmental factors (such as surface energy) of a catalyst can significantly alter catalytic performance. Thus, these two topics are mainly discussed for copper-based catalyst developments in this Account.Here, we provided a concise and comprehensive introduction to the well-established strategies employed for the design of copper-based electrocatalysts for CO2RR/CORR. We used several examples from our research group, as well as representative studies of other research groups in this field during the recent five years, with the perspectives of tuning local electron states, regulating alloy phases, modifying interfacial coverages, and adjusting other interfacial microenvironments (e.g., molecule modification or surface energy). Finally, we employed the techno-economic assessment with a viewpoint on the future application of CO2/CO electroreduction in manufacturing sustainable chemicals. Our study indicates that when carbon price is taken into account, the electrocatalytic CO2-to-chemical conversion can be more market-competitive, and several potential value-added products including formate, methanol, ethylene, and ethanol can all make profits under optimal operating conditions. Moreover, a downstream module employing traditional chemical industrial processes (e.g., thermal polymerization, catalytic hydrolysis, or condensation process) will also make the whole electrolysis system profitable in the future. These design principles, combined with the recent advances in the development of efficient copper-based electrocatalysts, may provide a low-cost and long-lasting catalytic system for a profitable industrial-scale CO2RR in the future

Weak-Field Electro-Flash Induced Asymmetric Catalytic Sites toward Efficient Solar Hydrogen Peroxide Production

Borocarbonitride (BCN), in a mesoscopic asymmetric state, is regarded as a promising photocatalyst for artificial photosynthesis. However, BCN materials reported in the literature primarily consist of symmetric N-[B]3 units, which generate highly spatial coupled electron–hole pairs upon irradiation, thus kinetically suppressing the solar-to-chemical conversion efficiency. Here, we propose a facile and fast weak-field electro-flash strategy, with which structural symmetry breaking is introduced on key nitrogen sites. As-obtained double-substituted BCN (ds-BCN) possesses high-concentration asymmetric [B]2–N-C coordination, which displays a highly separated electron–hole state and broad visible-light harvesting, as well as provides electron-rich N sites for O2 affinity. Thereby, ds-BCN delivers an apparent quantum yield of 7.6% at 400 nm and a solar-to-chemical conversion efficiency of 0.3% for selective 2e-reduction of O2 to H2O2, over 4-fold higher than that of the traditional calcined BCN analogue and superior to the metal-free C3N4-based photocatalysts reported so far. The weak-field electro-flash method and as-induced catalytic site symmetry-breaking methodologically provide a new method for the fast and low-cost fabrication of efficient nonmetallic catalysts toward solar-to-chemical conversions

Promoting CO₂ Electroreduction to Acetate by an Amine-Terminal, Dendrimer-Functionalized Cu Catalyst

Acetate derived from electrocatalytic CO2 reduction represents a potential low-carbon synthesis approach. However, the CO2-to-acetate activity and selectivity are largely inhibited by the low surface coverage of in situ generated *CO, as well as the inefficient ethenone intermediate formation due to the side reaction between CO2 and alkaline electrolytes. Tuning catalyst microenvironments by chemical modification of the catalyst surface is a potential strategy to enhance CO2 capture and increase local *CO concentrations, while it also increases the selectivity of side reduction products, such as methane or ethylene. To solve this challenge, herein, we developed a hydrophilic amine-tailed, dendrimer network with enhanced *CO intermediate coverage on Cu catalytic sites while at the same time retaining the in situ generated OH– as a high local pH environment that favors the ethenone intermediate toward acetate. The optimized amine-network coordinated Cu catalyst (G3-NH2/Cu) exhibits one of the highest CO2-to-acetate Faradaic efficiencies of 47.0% with a partial current density of 202 mA cm–2 at −0.97 V versus the reversible hydrogen electrode

Dual-Atomic Cu Sites for Electrocatalytic CO Reduction to C₂₊ Products

Monodispersed single metal atoms have been demonstrated with unique potentials for electroreduction of CO2 or CO, while the capability of producing multicarbon (C2+) products is still limited. In this work, we developed a dual metal atomic catalyst with uniform distributions of two adjacent Cu–Cu or Cu–Ni atoms anchored on nitrogen-doped carbon frameworks, featuring distinctive catalytic sites for CO electroreduction. Due to the synergistic effect between adjacent metal sites, the dual Cu–Cu atomic catalyst enables efficient CO electroreduction to C2+ products with an outstanding Faradaic efficiency of ∼91% and a high partial current density over 90 mA·cm–2. In contrast, the dual Cu–Ni atomic catalyst exhibits a remarkably different CO electroreduction selectivity mainly toward CH4. Theoretical calculations suggest that the dual Cu atomic sites facilitate the electroreduction of two CO molecules and subsequent carbon–carbon coupling toward ethylene and acetate, while the replacement of one of the dual Cu atoms with Ni results in too strong CO adsorption, and thus only the single Cu atom functions as the catalytic site for the C1 reduction pathway

Surface Energy Tuning on Cu/NC Catalysts for CO Electroreduction

Electrochemical CO reduction reaction (CORR) represents a potential approach to generate value-added products. Nonetheless, it is generally challenging for conventional measurements to quantify the catalytic surface properties, due to the geometric blockage and synergistic effect from the support. Herein, the surface energy of copper-loaded nitrogen-doped carbon (Cu/NC) was investigated by adsorption with specific functional groups using inverse gas chromatography (IGC). The dispersive component (γSD) and the acid/base character of the surface energy were determined using non-polar and polar probe molecules. The specific free energy (ΔGAB), the enthalpy of adsorption (ΔHAB), and the acidic (KA) and basic (KD) parameters were obtained, which allowed to provide the affinity information of intermediates such as *CHO, *OCH2COH, and *H. The surface energy analysis suggested that the Cu/N0.17C catalyst with the highest basic parameter (KD = 7.350) and optimal acid interaction (KA/KD ∼ 0.046) exhibited high catalytic performance in the acetate production, with a Faradaic efficiency (FE) of 63% and a partial current density of −330 mA·cm–2. The exposed catalytic sites on Cu/NC were suggested to activate H2O and stabilize oxygenate intermediates favorably for the electrochemical CO-to-acetate conversion

High-Power CO₂‑to‑C₂ Electroreduction on Ga-Spaced, Square-like Cu Sites

The electrochemical conversion of CO2 into multicarbon (C2) products on Cu-based catalysts is strongly affected by the surface coverage of adsorbed CO (*CO) intermediates and the subsequent C–C coupling. However, the increased *CO coverage inevitably leads to strong *CO repulsion and a reduced C–C coupling efficiency, thus resulting in suboptimal CO2-to-C2 activity and selectivity, especially at ampere-level electrolysis current densities. Herein, we developed an atomically ordered Cu9Ga4 intermetallic compound consisting of Cu square-like binding sites interspaced by catalytically inert Ga atoms. Compared to Cu(100) previously known with a high C2 selectivity, the Ga-spaced, square-like Cu sites presented an elongated Cu–Cu distance that allowed to reduce *CO repulsion and increased *CO coverage simultaneously, thus endowing more efficient C–C coupling to C2 products than Cu(100) and Cu(111). The Cu9Ga4 catalyst exhibited an outstanding CO2-to-C2 electroreduction, with a peak C2 partial current density of 1207 mA cm–2 and a corresponding Faradaic efficiency of 71%. Moreover, the Cu9Ga4 catalyst demonstrated a high-power (∼200 W) electrolysis capability with excellent electrochemical stability

Interfacial Synergy between the Cu Atomic Layer and CeO₂ Promotes CO Electrocoupling to Acetate

Cu is considered to be an effective electrocatalyst in CO/CO2 reduction reactions (CORR/CO2RR) because of its C–C coupling into C2+ products, but it still remains a formidable challenge to rationally design Cu-based catalysts for highly selective CO/CO2 reduction to C2+ liquid products such as acetate. We here demonstrate that spraying atomically layered Cu atoms onto CeO2 nanorods (Cu–CeO2) can lead to a catalyst with an enhanced acetate selectivity in CORR. Owing to the existence of oxygen vacancies (Ov) in CeO2, the layer of Cu atoms at interface coordinates with Ce atoms in the form of Cu–Ce (Ov), as a result of strong interfacial synergy. The Cu–Ce (Ov) significantly promotes the adsorption and dissociation of H2O, which further couples with CO to selectively produce acetate as the dominant liquid product. In the current density range of 50–150 mA cm–2, the Faradaic efficiencies (FEs) of acetate are over 50% with a maximum value of 62.4%. In particular, the turnover frequency of Cu–CeO2 reaches 1477 h–1, surpassing that of Cu nanoparticle-decorated CeO2 nanorods, bare CeO2 nanorods, as well as other existing Cu-based catalysts. This work advances the rational design of high-performance catalysts for CORR to highly value-added products, which may attract great interests in diverse fields including materials science, chemistry, and catalysis