Activating Kläui-Type Organometallic Precursors at Metal Oxide Surfaces for Enhanced Solar Water Oxidation

Activating molecular catalysts at the surface of metal oxides can be a promising strategy to overcome the sluggish interfacial kinetics and enhance the efficiencies for photo­(electro)­chemical (PEC) water oxidation. However, the physical association between inorganic semiconductors for PEC process and organometallic molecular catalysts for surface catalytic reactions generally remains a challenging problem. In the present work, Kläui-type organometallic precursor [Cp*Ir­{P­(O)­(OH)₂}₃]Na was first synthesized and subsequently successfully anchored onto BiVO₄ nanopyramids grown on transparent conducting substrates through various procedures. Treating the resulting hybrid heteronanostructure with IO₄^– induces a strong synergism between iridium atoms and BiVO₄ nanocrystals that exhibits a 5.5 times enhancement in photocurrent density at 1.23 V vs reversible hydrogen electrode (RHE) for PEC water oxidation. This simple approach provides an effective alternative pathway for molecular catalysts anchoring on inorganic semiconductors for efficient renewable energy utilization

Evolution of Visible Photocatalytic Properties of Cu-Doped CeO₂ Nanoparticles: Role of Cu²⁺-Mediated Oxygen Vacancies and the Mixed-Valence States of Ce Ions

We report the contribution of oxygen vacancies for enhancing the optical and visible photocatalytic properties of Cu-doped CeO₂ nanoparticles (NPs) synthesized through a low-temperature coprecipitation method. Doping Cu ions in the ceria lattice in different mole percentages, 0, 3, 5, 7, 9, and 15 wt %, results in enhancement of visible photocatalytic properties even under natural sunlight. Transmission electron microscopy and X-ray diffraction studies showcase the monodispersive nature of Cu-doped CeO₂ NPs in the size range of 3–7 nm with face-centered cubic structure. The Cu-based defect states induce a narrow band function in ceria nanostructures and influence the red shift in absorption with the Cu concentrations. Visible photocatalytic degradation of methylene blue was investigated in the presence of pure CeO₂ NPs, CuO NPs, and Cu-doped CeO₂ NPs. These studies revealed that the 7 wt % of Cu-doped CeO₂ NPs exhibit the degradation rates of 1.41 × 10^–2 and 1.12 × 10^–2 min^–1 under exposure to natural sunlight and visible light (Xe light source), respectively. This is nearly 23.5 and 1.61 times faster than the undoped CeO₂ and CuO NPs, respectively. The inclusion of more Cu²⁺ ions in the CeO₂ structure leads to the interaction and spatial distribution of oxygen vacancies with a Ce⁴⁺/Ce³⁺ ratio defect. This promotes the narrowing of the band function to the visible photocatalytic characteristics. Detailed investigations from X-ray absorption spectroscopy support the fact that the oxygen vacancies may strongly affect the valences of Ce ions in CeO₂, which improves the carrier mobility and visible response

X-ray Absorption Spectroscopic Study on Interfacial Electronic Properties of FeOOH/Reduced Graphene Oxide for Asymmetric Supercapacitors

[[abstract]]The effects of growth time and interface between the iron oxyhydroxide (FeOOH) and carbon materials (carbon nanotubes (CNT) and reduced graphene oxide (RGO)) to form an asymmetric supercapacitor was studied by X-ray absorption spectroscopy (XAS) and electrochemical measurements. FeOOH/CNT (FCNT) and FeOOH/RGO (FRGO) were successfully synthesized by a simple spontaneous redox reaction with FeCl3. The RGO functions as an ideal substrate, providing rich growth sites for FeOOH, and it is believed to facilitate the transport of electrons/ions across the electrode/electrolyte interface. FRGO has been identified as a supercapacitor and found to exhibit significantly greater capacitance than FCNT. To gain further insight into the effects of growth times and the interface of FeOOH for FCNT and FRGO, the electronic structures of FCNT and FRGO with various FeOOH growth times were elucidated by XAS. The difference between the surface electronic structures of CNT and RGO yields different nucleation and growth rates of FeOOH of FeOOH. RGO with excellent interface properties arises from a high degree of covalent functionalization, and/or defects make it favorable for FeOOH growth. FRGO is therefore a promising electrode material for use in the fabrication of asymmetric supercapacitors. In this work, coupled XAS and electrochemical measurements reveal the electronic structure of the interface between FeOOH and the carbon materials and the capacitance performance of asymmetric supercapacitors, which are very useful in the fields of nanomaterials and nanotechnology, especially for their applications in storing energy[[notice]]補正完

Atomically Dispersed Metal–Nitrogen–Carbon Catalysts with <i>d</i>‑Orbital Electronic Configuration-Dependent Selectivity for Electrochemical CO₂‑to-CO Reduction

A variety of atomically dispersed transition-metal-anchored nitrogen-doped carbon (M–N–C) electrocatalysts have shown encouraging electrochemical CO2 reduction reaction (CO2RR) performance, with the underlying fundamentals of central transition-metal atom determined CO2RR activity and selectivity yet remaining unclear. Herein, a universal impregnation-acid leaching method was exploited to synthesize various M–N–C (M: Fe, Co, Ni, and Cu) single-atom catalysts (SACs), which revealed d-orbital electronic configuration-dependent activity and selectivity toward CO2RR for CO production. Notably, Ni–N–C exhibits a very high CO Faradaic efficiency (FE) of 97% at −0.65 V versus RHE and above 90% CO selectivity in the potential range from −0.5 to −0.9 V versus RHE, much superior to other M–N–C (M: Fe, Co, and Cu). With the d-orbital electronic configurations of central metals in M–N–C SACs well elucidated by crystal-field theory, Dewar–Chatt–Duncanson (DCD) and differential charge density analysis reveal that the vacant outermost d-orbital of Ni2+ in a Ni–N–C SAC would benefit the electron transfer from the C atoms in CO2 molecules to the Ni atoms and thus effectively activate the surface-adsorbed CO2 molecules. However, the outermost d-orbital of Fe3+, Co2+, and Cu2+ occupied by unpaired electrons would weaken the electron-transfer process and then impede CO2 activation. In situ spectral investigations demonstrate that the generation of *COOH intermediates is favored over Ni–N–C SAC at relatively low applied potentials, supporting its high CO2-to-CO conversion performance. Gibbs free energy difference analysis in the rate-limiting step in CO2RR and hydrogen evolution reaction (HER) reveals that CO2RR is thermodynamically favored for Ni–N–C SAC, explaining its superior CO2RR performance as compared to other SACs. This work presents a facile and general strategy to effectively modulate the CO2-to-CO selectivity from the perspective of electronic configuration of central metals in M–N–C SACs