Yu-Jhih Shen

Electrochemical CO2 reduction reaction (CO2RR) offers a promising route to convert CO2 into value-added fuels and chemicals using renewable electricity. Cu-based catalysts are uniquely capable of producing C2+ hydrocarbons and oxygenates through C–C coupling, but their performance is limited by insufficient *CO coverage, broad product distributions, competing hydrogen evolution, and stability issues at high current densities. Tandem catalysis addresses these challenges by integrating CO-generating components with Cu-based C–C coupling sites. This review summarizes recent advances in Cu-based tandem catalysts under flow-cell and industrially relevant conditions, focusing on spatially separated systems, Ag–Cu bimetallic interfaces, single-atom alloys, and SAC–Cu tandem architectures. Key design principles include regulating CO generation, transport, interfacial structure, and coupling pathways.

Elucidating reaction intermediates under practically relevant conditions remains a fundamental challenge in electrocatalysis. For an electrochemical CO₂ reduction reaction (CO₂RR), reaction mechanisms can differ substantially between conventional H-cells and high-rate flow cells, complicating accurate operando characterization. In this study, we develop a flow-cell-compatible operando surface-enhanced Raman spectroscopy platform by integrating silica-coated Au nanorods (AuNRs@SiO₂) optimized for 785 nm excitation. The plasmonic resonance enhances Raman signals while suppressing fluorescence, and the inert SiO₂ shell prevents catalytic perturbation, enabling sensitive measurements under practical catalytic conditions. Using a benchmark copper catalyst, we directly detect key transient intermediates, including *CO₂^- and *HOCCOH, that are inaccessible by conventional Raman spectroscopy. Deconvolution of the adsorbed *CO reveals bridge-bonded, low-frequency, and high-frequency components, establishing a quantitative correlation between *CO speciation and C₂ selectivity. Parallel flow-cell and H-cell comparisons highlight the necessity of realistic mass transport. This work establishes a general operando spectroscopic strategy for mechanistic studies under realistic CO₂RR conditions.

Ag–Cu tandem catalysts are a promising route to boost C₂₊ formation during CO₂ electroreduction; however, well-defined layered Ag/Cu catalysts fabricated by PVD/sputtering without an ionomer behave like pure Cu in flow cells, showing no tandem enhancement. Contact-angle measurements indicate that the exposed Ag surface lowers overall hydrophobicity, restricting CO₂ transport to Ag and suppressing tandem pathways. To address this limitation, in this study, we adopt a hydrophobic surface modification using 1-dodecanethiol (DDT). The resulting DDT–Ag/Cu achieves 74.09 ± 1.69% Faradaic efficiency toward C₂₊ products with a partial current density of 370.5 ± 8.45 mA cm^–2 at 500 mA cm^–2, outperforming benchmark Cu and unmodified Ag/Cu under optimized conditions (by ∼65%). DDT–Ag/Cu also enhances ethanol selectivity, increasing the ethanol-to-ethylene ratio from ∼0.5 to ∼1.0. In situ Raman spectroscopy reveals distinct intermediates under hydrophobic conditions. These results clarify the intrinsic behavior of Ag–Cu tandem catalysis and offer a practical strategy to boost tandem performance in flow-cell CO₂ electroreduction.

Acidic electrochemical CO₂ reduction reaction (CO₂RR) offers an attractive route to store intermittent renewables as valuable chemicals with high carbon efficiency but suffers from low selectivity due to predominant hydrogen evolution reaction. Utilizing concentrated alkali cations steers the acidic CO₂RR to multicarbon (C₂₊) products but leads to salt precipitation. Here we report a molecular tuning strategy to facilitate acidic CO₂RR to ethylene under a low K⁺ concentration by modifying tetraphenylporphyrin-based molecules onto a Cu surface. At 200 mA cm^-2, we achieve a record ethylene Faradaic efficiency (FE) of 53% on 5,10,15,20-tetraphenyl-21H,23H-porphine zinc functionalized Cu catalysts (a 1.2× improvement compared to the best reports at above 100 mA cm^-2 under an acidic electrolyte having a low alkali cation concentration) and a high C₂₊ FE of 85%, as well as a high CO₂ single-pass utilization of 72%. This work presents a catalyst design strategy for efficient acidic CO₂-to-ethylene electrolysis under low alkali-cation availability.

Tuning of catalyst-support interactions potentially offers a powerful means to control activity. However, rational design of the catalyst support is challenged by a lack of clear property-activity relationships. Here, we uncover how the electronegativity of a support influences reaction pathways in electrochemical CO ₂ reduction. This was achieved by creating a model system consisting of Cu nanoparticles hosted on a series of carbon supports, each with a different heteroatom dopant of varying electronegativity. Notably, we discovered that dopants with high electronegativity reduce the electron density on Cu and induce a selectivity shift toward multicarbon (C ₂₊ ) products. With this design principle, we built a composite Cu and F-doped carbon catalyst that achieves a C ₂₊ Faradaic efficiency of 82.5% at 400 mA cm ⁻² , with stable performance for 44 hours. Using simulated flue gas, the catalyst attains a C ₂₊ FE of 27.3%, which is a factor of 5.3 times higher than a reference Cu catalyst.