The electrochemical CO₂ reduction reaction (CO₂RR) is a promising approach for converting CO₂ into valuable chemicals and promoting carbon cycling. Among the products of CO₂RR, ethylene (C₂H₄), as a crucial chemical feedstock, holds significant market demand and economic value. The design of an electrolyte-free cathode in membrane electrode assemblies (MEAs) can effectively mitigate mass transfer limitations, reduce ohmic losses, and enhance interfacial efficiency, thereby significantly improving current density and product selectivity. The integration of copper-based catalysts into MEAs is considered a promising strategy for the industrial-scale production of C₂H₄ via CO₂RR. However, comprehensive reviews on the application of copper-based catalysts in MEAs for CO₂RR to C₂H₄ remain limited, particularly regarding systematic analyses of catalyst design strategies, optimization of MEA components and operating conditions, and MEA device configurations. This review systematically summarizes the latest research progress on copper-based catalysts in MEAs for CO₂RR to C₂H₄. Firstly, the reaction mechanism of CO₂RR to C₂H₄ was summarized and the role of intermediate adsorption regulation was highlighted in MEA systems. Secondly, strategies applied to optimize ethylene production using copper-based catalysts in MEAs were also summarized accordingly. Next, the influence of components, operational conditions, and device design for MEA was discussed. Finally, the opportunities and challenges of using copper-based catalysts in MEAs for C₂H₄ production were outlined. This review aims to provide insights and inspire further research efforts toward optimizing the performance of CO₂RR to C₂H₄ in MEAs.

Renewable-energy-driven nitrate (NO₃⁻) electroreduction to ammonia (NH₃) (NERA) has been an attractive technology for decarbonizing NH₃ production and wastewater treatment. Improving NERA efficiency requires electrocatalysts that are earth-abundant and show fantastic performance. Here we report a semiempirical activity descriptor of e_g occupancy (of surface B-site cations) for identifying inexpensive perovskite oxides with extremely high efficacy toward NERA. We establish the descriptor by systematic investigations of more than 10 perovskite oxides. These investigations demonstrate that their intrinsic NERA activities display a volcano-shaped dependence on e_g occupancy and the optimized intrinsic activities are accessible at near-1 e_g occupancies. This could plausibly be attributed to the favorable overlaps between surface adsorbates and vertically-oriented e_g orbitals. More importantly, utilizing this descriptor, we predict a highly active, selective, and durable NERA electrocatalyst with a composition of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF). Because of its close-to-1 e_g occupancy (i.e. ~ 1.2), the BSCF features a superior NH₃ production rate of 0.12 g·h⁻¹·mg_cat.⁻¹ (Faradaic efficiency of 97.8%) that is at top of the volcano plot, and substantially outperforms most NERA electrocatalysts reported in literature.