We have revealed that cubelike and hexarhombic docadehedron-like Cu single crystals showed an enhancement of C2 products (ethylene and ethanol) while octahedron-like Cu nanoscale single crystals promoted C1 products of CO2 reduction. This product selectivity was revealed to be highly associated with the atomic arrangement on the surface. The remarkable high selectivity of ethanol (faraday efficiency of 25% with 14 mA/cm2, J ethanol ≈ 3.5 mA/cm2) for H–Cu was investigated and unraveled by using in situ X-ray absorption spectroscopy and density functional theory calculation. It was shown that the binding energy of adsorbed *O atom on the surface is substantial, which causes bifurcation of the reaction pathway and leads to the formation of ethanol.

In the face of climate change and rising energy consumption, the electrochemical oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and electrochemical CO2 reduction reaction (CO2RR) are promising catalytic processes...

Metal oxides of the spinel family have shown great potential towards the oxygen evolution reaction (OER), but the fundamental OER mechanism of spinel oxides is still far from being completely understood, especially for the role of the metal ions. Owing to various coordinated sites of divalent/trivalent metals ions and surface conditions (morphology and defects), it is a great challenge to have a fair assessment of the electrocatalytic performance of spinel systems. Herein, we demonstrated a series of MFeO (M = Fe, Co, Ni, Zn) with a well-controlled morphology to achieve a comprehensive study of electrocatalytic activity toward OER. By utilizing several in situ analyses, we could conclude a universal rule that the activities for OER in the metal oxide systems were determined by the occurrence of a phase transformation, and this structural transformation could work well in both crystallographic sites (T and O sites). Additionally, the divalent metal ion significantly dominated the formation of oxyhydroxide through an epitaxial relationship, which depended on the atomic arrangement at the interface of spinel and metal oxyhydroxide, while trivalent metal ions remained unchanged as a host lattice. The metal oxyhydroxide was formed during a redox reaction rather than being formed during OER. The occurrence of the redox reaction seems to accompany a remarkable increase in resistance and capacitance might result from the structural transformation from spinel to metal oxyhydroxide. We believe that the approaching strategies and information obtained in the present study can offer a guide to designing a promising electrocatalytic system towards the oxygen evolution reaction and other fields.

Atomically dispersed single-atom catalysts are among the most attractive electrocatalysts for the CO2 reduction reaction (CRR). To elucidate the origin of the exceptional activity of atomically dispersed Fe–N–C catalyst in CRR, we have performed operando 57Fe Mössbauer spectroscopic studies on a model single-Fe-atom catalyst with a well-defined N coordination environment. Combining with operando X-ray absorption spectroscopy, the in situ-generated four pyrrolic nitrogen atom-coordinated low-spin Fe­(I) (LS FeIN4) featuring monovalent iron is identified as the reactive center for the conversion of CO2 to CO. Furthermore, density functional theory calculations reveal that the optimal binding strength of CO2 to the LS FeIN4 site, with strong orbital interactions between the singly occupied d z 2 orbital of the Fe­(I) site and the singly occupied π* orbital of [COOH] fragment, is the key factor for the excellent CRR performance.

photosynthetic or solar-driven watersplitting systems, the oxygen evolution reaction (OER) is driven by a four-chargecarrier transfer pathway, while either carbon dioxide reduction or the hydrogen evolution reaction takes place on the counter electrode. However, this halfreaction (i.e., the OER) is regarded as the kinetic bottleneck for both artificial photosynthesis and overall water splitting because of the large energy requirements (i.e., large overpotentials) for driving the multielectron transfer processes. Fortunately, light-absorbing semiconductor devices that utilize small bandgap materials, such as Si, GaAs, or GaP, have been demonstrated to be efficient photoelectrodes for achieving high performance catalysis of the OER [5,6] owing to their wide absorption region in the visible light spectrum. Nevertheless, the utilization of these small band gap materials has commonly suffered from the considerable issue of their valance bands having characteristically low driving forces, thereby leading to poor transfer of the charge carriers needed for water oxidation. The dynamic behavior of the photoinduced charge-carrier separation is a critical factor for addressing both the overpotential requirement and poor driving force to effectively facilitate the transport of the excited minority carriers (i.e., holes) towardThe integration of surface metal catalysts with semiconductor absorbers to produce photocatalytic devices is an attractive method for achieving high-efficiency solar-induced water splitting. However, once combined with a photoanode, detailed discussions of the light-induced processes on metal/semiconductor junction remain largely inadequate. Here, by employing in situ X-ray scattering/ diffraction and absorption spectroscopy, the generation of a photoinduced adaptive structure is discovered at the interfacial metal-semiconductor (M-S) junction between a state-of-the-art porous silicon wire and nickel electrocatalyst, where oxygen evolution occurs under illumination. The adaptive layer in M-S junction through the light-induced activation can enhance the voltage by 247 mV (to reach a photocurrent density of 10 mA cm −2 ) with regard to the fresh photoanode, and increase the photocurrent density by six times at the potential of 1.23 V versus reversible reference electrode (RHE). This photoinduced adaptive layer offers a new perspective regarding the catalytic behavior of catalysts, especially for the photocatalytic water splitting of the system, and acting as a key aspect in the development of highly efficient photoelectrodes.