Effect of Surface Electron Trapping and Small Polaron Formation on the Photocatalytic Efficiency of Copper(I) and Copper(II) Oxides.

CuO, CuO, and mixed phase CuO/CuO represent promising candidates for photoelectrochemical H evolution due to their strong visible light absorption, earth-abundance, and chemical stability. However, the photoelectrochemical efficiency in these materials remains far below the theoretical limit, largely due to poorly understood surface electron dynamics. These dynamics depend on defect states, such as Cu atom vacancies and phase boundaries, which control electron trapping, charge carrier separation, and recombination.

Water-Mediated Charge Transfer and Electron Localization in a CoFe Cyanide-Bridged Trigonal Bipyramidal Complex.

The effects of temperature and chemical environment on a pentanuclear cyanide-bridged, trigonal bipyramidal molecular paramagnet have been investigated. Using element- and oxidation state-specific near-ambient pressure X-ray photoemission spectroscopy (NAP-XPS) to probe charge transfer and second order, nonlinear vibrational spectroscopy, which is sensitive to symmetry changes based on charge (de)localization coupled with DFT, a detailed picture of environmental effects on charge-transfer-induced spin transitions is presented. The molecular cluster, CoFe(tmphen)(μ-CN)(-CN), abbrev.

Direct observation of bicarbonate and water reduction on gold: understanding the potential dependent proton source during hydrogen evolution.

The electrochemical conversion of CO represents a promising way to simultaneously reduce CO emissions and store chemical energy. However, the competition between CO reduction (COR) and the H evolution reaction (HER) hinders the efficient conversion of CO in aqueous solution. In water, CO is in dynamic equilibrium with HCO, HCO , and CO .

Electronic Structure and Ultrafast Electron Dynamics in CuO Photocatalysts Probed by Surface Sensitive Femtosecond X-ray Absorption Near-Edge Structure Spectroscopy.

CuO is often employed as a photocathode for H evolution and CO reduction, but observed efficiency is still far below the theoretical limit. To bridge the gap requires understanding the CuO electronic structure; however, computational efforts lack consensus on the orbital character of the photoexcited electron. In this study, we measure the femtosecond XANES spectra of CuO at the Cu M and O L edges to track the element-specific dynamics of electrons and holes.

Comparing interfacial cation hydration at catalytic active sites and spectator sites on gold electrodes: understanding structure sensitive CO reduction kinetics.

Hydrated cations present in the electrochemical double layer (EDL) are known to play a crucial role in electrocatalytic CO reduction (COR), and numerous studies have attempted to explain how the cation effect contributes to the complex COR mechanism. COR is a structure sensitive reaction, indicating that a small fraction of total surface sites may account for the majority of catalytic turnover. Despite intense interest in specific cation effects, probing site-specific, cation-dependent solvation structures remains a significant challenge.

The Solvation-Induced Onsager Reaction Field Rather than the Double-Layer Field Controls CO Reduction on Gold.

The selectivity and activity of the carbon dioxide reduction (COR) reaction are sensitive functions of the electrolyte cation. By measuring the vibrational Stark shift of in situ-generated CO on Au in the presence of alkali cations, we quantify the total electric field present at catalytic active sites and deconvolute this field into contributions from (1) the electrochemical Stern layer and (2) the Onsager (or solvation-induced) reaction field. Contrary to recent theoretical reports, the COR kinetics does not depend on the Stern field but instead is closely correlated with the strength of the Onsager reaction field.

Opportunities for Electrocatalytic CO Reduction Enabled by Surface Ligands.

To achieve high selectivity in enzyme catalysis, nature carefully controls both the catalyst active site and the pocket or environment that mediates access and the geometry of a reactant. Despite the many advantages of heterogeneous catalysis, active sites on a surface are rarely defined with atomic precision, making it difficult to control reaction selectivity with the molecular precision of homogeneous systems. In colloidal nanoparticle synthesis, structural control is accomplished using a surface ligand or capping layer that stabilizes a specific particle morphology and prevents nanoparticle aggregation.

Effect of surface ligands on gold nanocatalysts for CO reduction.

Nanoparticle catalysts display optimal mass activity due to their high surface to volume ratio and tunable size and structure. However, control of nanoparticle size requires the presence of surface ligands, which significantly influence catalytic performance. In this work, we investigate the effect of dodecanethiol on the activity, selectivity, and stability of Au nanoparticles for electrochemical carbon dioxide reduction (COR).

Role of Extracellular Polymeric Substances in a Methane Based Membrane Biofilm Reactor Reducing Vanadate.

For the first time, we demonstrated vanadate (V(V)) reduction in a membrane biofilm reactor (MBfR) using CH as the sole electron donor. The V(V)-reducing capability of the biofilm kept increasing, with complete removal of V(V) achieved when the influent surface loading of V(V) was 363 mg m day. Almost all V(V) was reduced to V(IV) precipitates, which is confirmed by a scanning electron microscope coupled to energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS).

The effect of electron competition on chromate reduction using methane as electron donor.

We studied the effect of electron competition on chromate (Cr(VI)) reduction in a methane (CH)-based membrane biofilm reactor (MBfR), since the reduction rate was usually limited by electron supply. A low surface loading of SO promoted Cr(VI) reduction. The Cr(VI) removal percentage increased from 60 to 70% when the SO loading increased from 0 to 4.