Photoinduced Charge Storage with p‑Type NiO Nanoplates via Surface Trapped Holes

Existing photoelectrochemical cells for solar energy conversion are hindered by their inability to counteract the ever-changing sunlight conditions, which results in unstable electrical energy output for production of chemicals. Herein, a p-type NiO nanoplate thin film photocathode with rich Ni vacancies is reported, enabling the dual functions of sunlight harvesting and electrical energy storage in a single material system. Band gap excitation of NiO induces surface adsorptions of hydroxide anions and a concomitant storage of in situ-generated photogenerated holes to form NiOOH. In the absence of light, the stored energy in NiOOH is discharged to provide a sustainable current by desorbing the hydroxide anions. The energy storage capacities of the NiO depend on the electrolyte pH and the magnitude of the applied bias. The energy storage capacities of the NiO are greater with alkaline electrolytes due to the availability of hydroxide anions for maintaining the overall charge neutrality in the electrode system. In addition, a sufficiently large negative bias is also required during periodic irradiation to enhance the charge separation efficiency and enable photogenerated holes to be available for charge storage. The feasibility for light-to-electrical energy storage with a single material photocathode is demonstrated, which provides a versatile solution to mitigate the instability of solar irradiation

Surface Structure of Pt-Modified Au Nanoparticles and Electrocatalytic Activity in Formic Acid Electro-Oxidation

Platinum-modified Au nanoparticles on a carbon support were prepared using carbon-supported Au nanoparticles as a substrate and a successive reduction process. These nanoparticles were applied as an electrocatalyst for formic acid electro-oxidation. The uniform Pt-modified Au nanoparticles (<5 nm in diameter) were highly dispersed on the carbon particles, and the Au surface was deposited with nanoscaled Pt. The Pt-modified Au nanoparticles showed higher electrocatalytic activities than the pure Pt electrocatalyst in the area- and mass-specific current densities. These results might be due to the enhancement effect of Au atoms and the high Pt utilization in the formic acid electro-oxidation reaction

Subnanometer Cu Clusters on Porous Ag Enhancing Ethanol Production in Electrochemical CO₂ Reduction

Controlling the electrochemical CO2 reduction process for multicarbon production is challenging. Ethanol is typically produced with lower selectivity compared to ethylene. In addition, ill-defined catalytic active sites and elusive mechanisms of C–C coupling further hinder the enhancement of ethanol generation. Here, we carefully regulated the quantity of the Cu atoms and deposited them onto a Ag inverse-opal structure (AgIOs) using the pulse-electrodeposition method. Subnanometer Cu clusters demonstrated a 2.5 times higher Faradaic efficiency for ethanol production compared to that for ethylene at −1.05 V vs RHE. Conversely, as the size of Cu increased to nanometers, ethylene became the dominant product. Excessive adsorption of CO on Cu clusters, which migrates from the Ag surface, is attributed to the improved ethanol production. Abundant Ag/Cu boundaries and adjacent spacing between Ag and Cu clusters may enhance the surface migration of CO. In contrast, the preferential site-selective CO adsorption on large Cu nanoparticles is associated with solution-mediated CO migration. Operando shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) revealed a high coverage of the CO on the Cu clusters. The initial intermediate *OCCOH by C–C coupling appeared for both Cu clusters and nanoparticles. However, Cu clusters accommodated more carbonaceous intermediates, highlighting the critical role of CO and intermediate coverages on Cu in ethanol production

Effect of Surface Segregation on the Methanol Oxidation Reaction in Carbon-Supported Pt−Ru Alloy Nanoparticles

Ru and Pt−Ru (Pt:Ru = 1:1) nanoparticles supported on carbon black were prepared by the borohydride reduction method using oleylamine as a stabilizer in an anhydrous ethanol solvent. We investigated the effect of Pt segregation to the surface of alloy nanoparticles on the methanol oxidation reaction (MOR). As-prepared Pt1Ru1/C showed a narrow size distribution and a relatively uniform particle distribution on a carbon support. However, its electrocatalytic activity toward the MOR was poor due to the high surface concentration of Ru. As duration time of heat treatment at 200 °C was increased up to 2 h, the surface composition of Pt atoms was increased without significant particle growth due to thermally induced segregation of Pt atoms, which were revealed by TEM images, X-ray photoelectron spectroscopy (XPS) analysis, changes in the potentials of zero total charge (pztc), and increase in the oxidation charge of “reduced CO2”. In particular, from the combination of CO adlayer oxidation and “reduced CO2” oxidation charges, the increased surface concentration of Pt of alloy catalysts was relatively quantified when compared to its as-prepared state. Cyclic voltammograms in 0.1 M HClO4 solution with 0.5 M methanol showed that Pt1Ru1/C annealed for 2 h at 200 °C in a flow of mixture gas of Ar and H2 (5 vol %) had a less positive onset potential for the MOR. These results demonstrate a definitive contribution from segregation of Pt atoms to the MOR activity

Oxygen-Vacancy-Driven Orbital Reconstruction at the Surface of TiO₂ Core–Shell Nanostructures

Oxygen vacancies and their correlation with the electronic structure are crucial to understanding the functionality of TiO2 nanocrystals in material design applications. Here, we report spectroscopic investigations of the electronic structure of anatase TiO2 nanocrystals by employing hard and soft X-ray absorption spectroscopy measurements along with the corresponding model calculations. We show that the oxygen vacancies significantly transform the Ti local symmetry by modulating the covalency of titanium–oxygen bonds. Our results suggest that the altered Ti local symmetry is similar to the C3v, which implies that the Ti exists in two local symmetries (D2d and C3v) at the surface. The findings also indicate that the Ti distortion is a short-range order effect and presumably confined up to the second nearest neighbors. Such distortions modulate the electronic structure and provide a promising approach to structural design of the TiO2 nanocrystals

Na₂ZrFe(PO₄)₃A Rhombohedral NASICON-Structured Material: Synthesis, Structure and Na-Intercalation Behavior

A NASICON-structured earth-abundant mixed transition metal (TM) containing Na-TM-phosphate, viz., Na2ZrFe(PO4)3, has been prepared via a sol–gel route using a low-cost Fe3+-based precursor. The as-prepared material crystallizes in the desired rhombohedral NASICON structure (space group: R3̅c) at room temperature. Synchrotron X-ray diffraction (XRD), transmission electron microscopy, X-ray absorption spectroscopy, etc., have been performed to determine the crystal structure, associated details, composition, and electronic structures. In light of the structural features, as one of the possible functionalities of Na2FeZr(PO4)3, Na-intercalation/deintercalation has been examined, which indicates the occurrence of reversible electrochemical Na-insertion/extraction via Fe2+/Fe3+ redox at an average potential of ∼2.5 V. The electrochemical data and direct evidences from operando synchrotron XRD indicate that the rhombohedral structure is preserved during Na-insertion/extraction, albeit within a certain range of Na-content (i.e., ∼2–3 p.f.u.), beyond which rhombohedral → monoclinic transformation takes place. Within this range, Na-insertion/extraction takes place via solid-solution pathway, resulting in outstanding cyclic stability, higher Na-diffusivity, and good rate-capability. To the best of the authors’ knowledge, this represents the first in-depth structural, compositional, and electrochemical studies with Na2ZrFe(PO4)3, along with the interplay between those, which provide insights into the design of similar low-cost materials for various applications, including sustainable electrochemical energy storage systems

Precisely Constructing Orbital Coupling-Modulated Dual-Atom Fe Pair Sites for Synergistic CO₂ Electroreduction

Electrochemical reduction of CO2 (CO2RR) provides an attractive pathway to achieve a carbon-neutral energy cycle. Single-atom catalysts (SAC) have shown unique potential in heterogeneous catalysis, but their structural simplicity prevents them from breaking linear scaling relationships. In this study, we develop a feasible strategy to precisely construct a series of electrocatalysts featuring well-defined single-atom and dual-site iron anchored on nitrogen-doped carbon matrix (Fe1–N–C and Fe2–N–C). The Fe2–N–C dual-atom electrocatalyst (DAC) achieves enhanced CO Faradaic efficiency above 80% in wider applied potential ranges along with higher turnover frequency (26,637 h–1) and better durability compared to SAC counterparts. Furthermore, based on in-depth experimental and theoretical analysis, the orbital coupling between the iron dual sites decreases the energy gap between antibonding and bonding states in *CO adsorption. This research presents new insights into the structure–performance relationship on CO2RR electrocatalysts at the atomic scale and extends the application of DACs for heterogeneous electrocatalysis and beyond

Influence of Oxide on the Oxygen Reduction Reaction of Carbon-Supported Pt−Ni Alloy Nanoparticles

Pt−Ni alloy nanoparticles supported on carbon black (Pt:Ni = 1:1) were prepared by the borohydride reduction method using acetate anions as a stabilizer in anhydrous ethanol solvent. Here, we surveyed the effect of oxide phases in Pt−Ni alloy nanoparticles on the electrocatalytic activity toward oxygen reduction reaction (ORR). As-prepared Pt1Ni1/C, which showed a relatively high degree of alloying, possessed the lower oxygen reduction reaction (ORR) activity as compared to pure Pt. However, following heat treatment in a flow of Ar at 300 °C for 3 h, Pt1Ni1/C showed oxygen reduction activity higher than that of commercial Pt/C (40 wt % Pt/C, Johnson-Matthey). The potential of zero total charge (PZTC) was calculated from cyclic voltammograms and the CO-displacement charge at dosing potentials at which anions are the main adsorbed species. The calculated value then shifted to a more positive potential after heat treatment. This indicates that the surface of the Pt−Ni nanoparticles became less oxophilic mainly due to the clustering of Pt. This anodic shift of the PZTC is consistent with the results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption near-edge structure spectroscopy (XANES). Consequently, the observed catalytic enhancement by heat treatment is due to the increase of metallic Pt and NiO and the phase separation between metallic Pt and Ni oxides

Hollow Nanostructured Metal Silicates with Tunable Properties for Lithium Ion Battery Anodes

Hollow nanostructured materials have attracted considerable interest as lithium ion battery electrodes because of their good electrochemical properties. In this study, we developed a general procedure for the synthesis of hollow nanostructured metal silicates via a hydrothermal process using silica nanoparticles as templates. The morphology and composition of hollow nanostructured metal silicates could be controlled by changing the metal precursor. The as-prepared hierarchical hollow nanostructures with diameters of ∼100–200 nm were composed of variously shaped primary particles such as hollow nanospheres, solid nanoparticles, and thin nanosheets. Furthermore, different primary nanoparticles could be combined to form hybrid hierarchical hollow nanostructures. When hollow nanostructured metal silicates were applied as anode materials for lithium ion batteries, all samples exhibited good cyclic stability during 300 cycles, as well as tunable electrochemical properties