Dynamic (Sub)surface-Oxygen Enables Highly Efficient Carbonyl-Coupling for Electrochemical Carbon Dioxide Reduction.

Nowadays, high-valent Cu species (i.e., Cuδ +) are clarified to enhance multi-carbon production in electrochemical CO2 reduction reaction (CO2RR). Nonetheless, the inconsistent average Cu valence states are reported to significantly govern the product profile of CO2RR, which may lead to misunderstanding of the enhanced mechanism for multi-carbon production and results in ambiguous roles of high-valent Cu species. Dynamic Cuδ + during CO2RR leads to erratic valence states and challenges of high-valent species determination. Herein, an alternative descriptor of (sub)surface oxygen, the (sub)surface-oxygenated degree (κ), is proposed to quantify the active high-valent Cu species on the (sub)surface, which regulates the multi-carbon production of CO2RR. The κ validates a strong correlation to the carbonyl (*CO) coupling efficiency and is the critical factor for the multi-carbon enhancement, in which an optimized Cu2O@Pd2.31 achieves the multi-carbon partial current density of ≈330 mA cm-2 with a faradaic efficiency of 83.5%. This work shows a promising way to unveil the role of high-valent species and further achieve carbon neutralization.

Activating dynamic atomic-configuration for single-site electrocatalyst in electrochemical CO2 reduction.

One challenge for realizing high-efficiency electrocatalysts for CO2 electroreduction is lacking in comprehensive understanding of potential-driven chemical state and dynamic atomic-configuration evolutions. Herein, by using a complementary combination of in situ/operando methods and employing copper single-atom electrocatalyst as a model system, we provide evidence on how the complex interplay among dynamic atomic-configuration, chemical state change and surface coulombic charging determines the resulting product profiles. We further demonstrate an informative indicator of atomic surface charge (φe) for evaluating the CO2RR performance, and validate potential-driven dynamic low-coordinated Cu centers for performing significantly high selectivity and activity toward CO product over the well-known four N-coordinated counterparts. It indicates that the structural reconstruction only involved the dynamic breaking of Cu-N bond is partially reversible, whereas Cu-Cu bond formation is clearly irreversible. For all single-atom electrocatalysts (Cu, Fe and Co), the φe value for efficient CO production has been revealed closely correlated with the configuration transformation to generate dynamic low-coordinated configuration. A universal explication can be concluded that the dynamic low-coordinated configuration is the active form to efficiently catalyze CO2-to-CO conversion.

Lewis Acidic Support Boosts C-C Coupling in the Pulsed Electrochemical CO2 Reaction.

Copper-oxide electrocatalysts have been demonstrated to effectively perform the electrochemical CO2 reduction reaction (CO2RR) toward C2+ products, yet preserving the reactive high-valent CuOx has remained elusive. Herein, we demonstrate a model system of Lewis acidic supported Cu electrocatalyst with a pulsed electroreduction method to achieve enhanced performance for C2+ products, in which an optimized electrocatalyst could reach ∼76% Faradaic efficiency for C2+ products (FEC2+) at ∼-0.99 V versus reversible hydrogen electrode, and the corresponding mass activity can be enhanced by ∼2 times as compared to that of conventional CuOx. In situ time-resolved X-ray absorption spectroscopy investigating the dynamic chemical/physical nature of Cu during CO2RR discloses that an activation process induced by the KOH electrolyte during pulsed electroreduction greatly enriched the Cuδ+O/Znδ+O interfaces, which further reveals that the presence of Znδ+O species under the cathodic potential could effectively serve as a Lewis acidic support for preserving the Cuδ+O species to facilitate the formation of C2+ products, and the catalyst structure-property relationship of Cuδ+O/Znδ+O interfaces can be evidently realized. More importantly, we find a universality of stabilizing Cuδ+O species for various metal oxide supports and to provide a general concept of appropriate electrocatalyst-Lewis acidic support interaction for promoting C2+ products.

Hetero-Atomic Pairs with a Distal Fe3+ -Site Boost Water Oxidation.

The hetero-atomic interaction has been the subject of many investigations, due to their heterogeneity, the individual roles of the atoms are still difficult to realize. Herein, an electrocatalyst with a hetero-atomic pair confined on a tungsten phosphide (WP) substrate so that the Fe3+ -site of the pair is distal to the surface is shown to deliver an extremely low overpotential of 192 mV at 10 mA cm-2 and one of the highest oxygen production turnover frequencies (TOF) of 2.1 s-1 at 300 mV under alkaline environment for the oxygen evolution reaction (OER). Operando characterization shows the Lewis acidic Fe3+ site boosts a large population of Co4+/3+ and the deprotonation of coordinated water, allowing simultaneously enhanced electron-transfer as well as the proton-transfer. A significant contribution from the WP substrate modulates the order of hydroxide transfer in the pre-equilibrium step (PES) and rate-determining-step (RDS), leading to a remarkable OER performance.

In Situ Identifying the Dynamic Structure behind Activity of Atomically Dispersed Platinum Catalyst toward Hydrogen Evolution Reaction.

Single-atom catalysts (SAs) with the maximum atom utilization and breakthrough activities toward hydrogen evolution reaction (HER) have attracted considerable research interests. Uncovering the nature of single-atom metal centers under operating electrochemical condition is highly significant for improving their catalytic performance, yet is poorly understood in most studies. Herein, Pt single atoms anchoring on the nitrogen-carbon substrate (PtSA /N-C) as a model system are utilized to investigate the dynamic structure of Pt single-atom centers during the HER process. Via in situ/operando synchrotron X-ray absorption spectroscopy and X-ray photoelectron spectroscopy, an intriguing structural reconstruction at atomic level is identified in the PtSA /N-C when it is subjected to the repetitive linear sweep voltammetry and cyclic voltammetry scanning. It demonstrates that the PtN bonding tends to be weakened under cathodic potentials, which induces some Pt single atoms to dynamically aggregate into forming small clusters during the HER reaction. More importantly, experimental evidence and/or indicator is offered to correlate the observed Tafel slope with the dynamic structure of Pt catalysts. This work provides an evident understanding of SAs under electrocatalytic process and offers informative insights into constructing efficient catalysts at atomic level for electrochemical water-splitting system.

Revealing the structural transformation of rutile RuO2via in situ X-ray absorption spectroscopy during the oxygen evolution reaction.

RuO2 has been generally considered as the most active catalyst for the oxygen evolution reaction (OER) to date and shows remarkably higher activity in an acidic electrolyte than under alkaline conditions. Nevertheless, the dynamic valence state and local structure of reactive centers (i.e., Ru) in both acidic and alkaline electrolytes have not been systematically investigated yet, especially through in situ approaches. Herein, we employed in situ X-ray absorption spectroscopy to study the dynamic valence state and local structure of RuO2 during the OER in both acidic and alkaline electrolytes. In the acidic electrolyte, the Ru center was reduced near the onset potential prior to launching the OER and was oxidized during the OER process, while the coordination numbers and the bond lengths of the Ru-O path also decreased as revealed by in situ EXAFS analysis. Besides, in the alkaline electrolyte, RuO2 showed a similar behavior as revealed under acidic conditions. These results provide an evident insight into the dynamic change of the RuO2 electrocatalyst during the OER.