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Electrochemistry and X-ray absorption spectroscopy (XAS) of MnO2/reduced graphene oxide (RGO) were made to evaluate capacitive performance and electronic structure as a supercapacitor. MnO2 was deposited on the surface of RGO by a spontaneous redox reaction. At low current density (1 A g−1), the specific capacitance of MnO2/RGO (MRGO) greatly increased with increasing growth time from 281 to 462 F g−1. Electrochemical results show that the specific capacitance of RGO and MRGO arises from the combined contributions of electrochemical double-layer capacitance (EDLC) and pseudo-capacitance. To gain insights into the charge storage mechanism of RGO and MRGO, it was characterized using ex-situ soft XAS techniques at Mn L-edge and C, O K-edges in the charging/discharging process. The ex-situ soft XAS results provide evidence that the contribution of RGO to specific capacitance involves an oxygen-functionality-related contribution of pseudocapacitance and EDLC. In addition, the specific capacitance of MRGO reveals pseudocapacitive contributions from the redox processes that involve the Mn(III)/Mn(IV) redox reaction in MnO2. This work utilizes electrochemical and ex-situ XAS techniques to elucidate charge storage mechanism for supercapacitor applications.

The mechanism of insertion/extraction of Al3+ ions in MoO3 with various crystal structures was characterized by in situ XRD and XAS techniques.

Supramolecular interactions have been found to be essential for exceptional electrochemical performance of a close-packed metal–organic-based cathode, considered one of the best ever reported.

Bismuth oxyhalides (BiOX, X = F, Cl, Br, I) are emerging energy materials because of their remarkable catalytic activity. The BiOX compounds usually have a tetragonal type crystal structure with unique layered morphology consisting of [X-Bi-O-Bi-X] sheets. Although the BiOX nanosheets exposed with {001} facets perform superior photoactivity, there is lack of understanding about their capability in the electrochemical CO2 reduction reaction (CO2RR). Herein, we adopt wet-chemical syntheses to make 2D BiOCl and Pd-doped BiOCl nanosheets for CO2RR. In the results, formic acid is the only one kind of product converted from CO2 along with H2 gas from water reduction over both BiOCl and Pd-doped BiOCl nanosheets. By thorough analyses with ex situ and in situ spectroscopy, the results reflect that (1) metallic Bi0 atoms generated by the applied negative potentials serve as the catalytic sites for the hydrogen evolution reaction (HER) and CO2RR and (2) the existence of doped Pd ions in the BiOCl structure reduces the barrier of charge transfer over the nanosheets, which enhances HER and CO2RR activities. We believe that the observations are important references for making catalysts toward CO2RR performance.

We present a detailed structural and optical analysis of dopant occupancy in Dy-doped Gd2O3 NPs not previously reported.

Summary Noble metals are considered a key branch of electrocatalysts. Unfortunately, their contributions to anodic reactions still face a big challenge. Here, guided by density functional theory, significant breakthroughs have been achieved by constructing a unique spontaneously oxidized interface in noble metal sub-nanocluster (SNC) catalysts depending on strong surface affinity. The spontaneous oxide interfaces with the amorphous covering on the rhodium (Rh) SNCs (diameter

Metal halide perovskites have attracted great attention for their superior light energy conversion applications. Herein, we demonstrated a facile synthesis of zero-dimensional Sn2+ perovskite Cs4-xMxSnBr6(M = K+ and Rb+) material through the cation transformation reaction at room temperature. Cs4SnBr6 NCs was mixed with pure metal bromide salts (KBr and RbBr) via the mechanochemical process to successfully synthesize Cs4-xMxSnBr6 perovskite where transformation of Cs to mixed Cs/Rb and mixed Cs/K was achieved. By substituting different cations, the bright fluorescence of the Cs4-xMxSnBr6 was tuned from dim green to greenish-cyan while achieving the photoluminescence (PL) quantum yield of ∼39%. The crystal structure of Sn based perovskite with the substitution of K+ or Rb+ cations was determined by X-ray diffraction (XRD). Moreover, the Cs4-xMxSnBr6 demonstrated superior air stability and exhibited a better photocatalytic activity for CO2 reduction reaction (CO2RR) with high selectivity of CH4 gas with a higher yield rate compared to the pristine Cs4SnBr6 NCs.

Thermoelectric materials capable of converting waste heat energy into electrical energy are enchanting for applications in wearable electronics and sensors by harvesting heat energy of the human body. Organic conducting polymers offer promise of thermoelectric materials for next-generation power sources of wearable devices due to their low cost in preparation, easy processing, low toxicity, low thermal conductivity, mechanical flexibility, light weight, and large area application. Generally, the pristine PEDOT:PSS film has low electrical conductivity, small Seebeck coefficient, and low thermal conductivity. The thermoelectric power factors of conducting polymers of p-type PEDOT:PSS films are considerably improved via synergistic effect by using ethylene glycol and reductants of EG/NaBH4 or EG/NaHCO3. As such, the charge carrier concentration of PEDOT:PSS films is tuned. The synergistic effect might lead to enhanced variation of density of states at the Fermi level and hence enhanced Seebeck coefficient. The resulting PEDOT:PSS films were characterized by atomic force microscopy (AFM), Raman spectroscopy, and XPS spectroscopy. The electrical conductivity and Seebeck coefficient were measured between 325 and 450 K. The carrier concentration and mobility were obtained by Hall measurements. The pristine thin film treated with 0.05 M EG/NaHCO3 solution exhibits the highest power factor of 183 μW m-1 K-2 at 450 K among these two series of films due to its significant enhanced Seebeck coefficient of 48 μV/K. The maximum output power of 121.08 nW is attained at the output voltage of 6.98 mV and the output current of 17.45 μA. The corresponding maximum power density is 98 μW/cm2 for a power generation device made of four pairs of p-leg (EG/NaHCO3 post-treated PEDOT:PSS) and n-leg (Cu0.6Ni0.4) on the polyamide substrate with the size of 4 mm × 20 mm for each leg.

We successfully prepared nitrogen-doped defective carbon spheres (Mo-N

A facile approach to synthesize a Pt-doped metal-organic framework (MOF)-derived layered double hydroxide (LDH), denoted as Pt@CuFe-LDHm, is developed. It consists of highly dispersed 2D nanosheets, and the excellent properties (high specific surface area and large porosity) inherited from CuFe(dobpdc) bestow it with superior catalytic properties. Pt@CuFe-LDHm shows low overpotentials of 33, 47 and 120 mV at 10 mA cm

We demonstrated how the special synergy between a noble metal single site and neighboring oxygen vacancies provides an "ensemble reaction pool" for high hydrogen generation efficiency and carbon dioxide (CO2) selectivity of a tandem reaction: methanol steam reforming. Specifically, the hydrogen generation rate over single site Ru1/CeO2 catalyst is up to 9360 mol H2 per mol Ru per hour (579 mLH2 gRu-1 s-1) with 99.5% CO2 selectivity. Reaction mechanism study showed that the integration of metal single site and O vacancies facilitated the tandem reaction, which consisted of methanol dehydrogenation, water dissociation, and the subsequent water gas shift (WGS) reaction. In addition, the strength of CO adsorption and the reaction activation energy difference between methanol dehydrogenation and WGS reaction play an important role in determining the activity and CO2 selectivity. Our study paves the way for the further rational design of single site catalysts at the atomic scale. Furthermore, the development of such highly efficient and selective hydrogen evolution systems promises to deliver highly desirable economic and ecological benefits.

The new TPS 44A beamline at the Taiwan Photon Source is presented. The beamline is equipped with a new quick-scanning monochromator (Q-Mono), which can provide both conventional step-by-step scans and on-the-fly scans for XAFS spectroscopy experiments, including XANES and EXAFS spectral measurements., The new TPS 44A beamline at the Taiwan Photon Source, located at the National Synchrotron Radiation Research Center, is presented. This beamline is equipped with a new quick-scanning monochromator (Q-Mono), which can provide both conventional step-by-step scans (s-scans) and on-the-fly scans (q-scans) for X-ray absorption fine-structure (XAFS) spectroscopy experiments, including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectral measurements. Ti and Te K-edge XAFS spectra were used to demonstrate the capability of collecting spectra at the limits of the working energy range. The Ni and Cu K-edge XAFS spectra for a Cu-doped Pt/Ni nanocomposite were acquired to test the performance of the newly commissioned beamline. Pt L 3- and Ru K-edge quick-scanning XAFS (QXAFS) spectra for standard Pt and Ru foils, respectively, revealed the stability of the q-scan technique. The results also demonstrated the beamline’s ability to collect XAFS spectra on a sub-second timescale. Furthermore, a Zn(s)|Zn2+ (aq)|Cu(s) system was tested to indicate that the states of the Zn electrode could be observed in real time for charging and discharging conditions using an in situ/operando setup combined with QXAFS measurements.

Ni-rich high-energy-density lithium ion batteries pose great risks to safety due to internal short circuits and overcharging; they also have poor performance because of cation mixing and disordering problems. For Ni-rich layered cathodes, these factors cause gas evolution, the formation of side products, and life cycle decay. In this study, a new cathode electrolyte interphase (CEI) for Ni2+ self-oxidation is developed. By using a branched oligomer electrode additive, the new CEI is formed and prevents the reduction of Ni3+ to Ni2+ on the surface of Ni-rich layered cathode; this maintains the layered structure and the cation mixing during cycling. In addition, this new CEI ensures the stability of Ni4+ that is formed at 100% state of charge in the crystal lattice at high temperature (660 K); this prevents the rock-salt formation and the over-reduction of Ni4+ to Ni2+. These findings are obtained using in situ X-ray absorption spectroscopy, operando X-ray diffraction, operando gas chromatography-mass spectroscopy, and X-ray photoelectron spectroscopy. Transmission electron microscopy reveals that the new CEI has an elliptical shape on the material surface, which is approximately 100 nm in length and 50 nm in width, and covers selected particle surfaces. After the new CEI was formed on the surface, the Ni2+ self-oxidation gradually affects from the surface to the bulk of the material. It found that the bond energy and bond length of the Ni-O are stabilized, which dramatically inhibit gas evolution. The new CEI is successfully applied in a Ni-rich layered compound, and the 18650- and the punch-type full cells are fabricated. The energy density of the designed cells is up to 300 Wh/kg. Internal short circuit and overcharging safety tests are passed when using the standard regulations of commercial evaluation. This new CEI technology is ready and planned for future applications in electric vehicle and energy storage.

Single-atom nickel catalysts hold great promise for photocatalytic water splitting due to their plentiful active sites and cost-effectiveness. Herein, we adopt a reactive-group guided strategy to prepare atomically dispersed nickel catalysts on red phosphorus. The hydrothermal treatment of red phosphorus leads to the formation of P-H and P-OH groups, which behave as the reactive functionalities to generate the dual structure of single-atom P-Ni and P-O-Ni catalytic sites. The produced single-atom sites provide two different functions: P-Ni for water reduction and P-O-Ni for water oxidation. Benefitting from this specific Janus structure, Ni-red phosphorus shows an elevated hydrogen evolution rate compared to Ni nanoparticle-modified red phosphorus under visible-light irradiation. The hydrogen evolution rate was additionally enhanced with increased reaction temperature, reaching 91.51 μmol h

The downsizing of catalysts to the atomic scale or subnanometer size can effectively maximize the atomic utilization and enhance the electrocatalytic activity. Carbon-supported Pt single atoms or sub-nanometer-sized Pt clusters (Ptc/C) are promising catalysts for the electrocatalytic hydrogen evolution reaction (HER). However, critical challenges remain in the mass production of high-quality Ptc/C catalysts. Herein, we report a facile synthesis method to achieve highly dispersed and highly dense Ptcs (average diameter of ∼0.4 nm) on various carbon supports (CSs). A tannic acid (TA) monolayer (TAi)-functionalized CS surface was achieved through π–π interactions without destroying the conjugated structure of CSs. TAi aids the adsorption of the Ptc precursor monolayer on CSs in a facile impregnation process. Notably, the thermally treated TA fragment-stabilized Ptcs strongly anchored to the carbon surface to form a highly thermostable Ptc/C catalyst, reported here for the first time. The synthesized Ptc/C catalyst (Ptc(250)/C) exhibits an exceptionally high Pt mass activity (imPt)/turnover frequency (TOF) at η = 60 mV (154.5 A mg−1/156.1 s−1), which are ∼106 times higher than those of commercial Pt/C (1.46 A mg−1/1.48 s−1) and superior to those of the state-of-the-art Pt-based catalysts.

There have been several studies on the catalytic activity of the hydrogen evolution reaction (HER) using ultralow loading of Pt catalysts or even Pt single atom catalysts. However, Pt single atom deposited on the surface of the carbon or metal oxide material has some drawbacks, such as high possibility of Pt desorption from the supported material in the electrolyte. Besides, from the reaction mechanism perspective, each Pt atom in this type of catalyst is too far to achieve high HER efficiency via the Tafel reaction pathway. In this work, gold nanodendrites (Au NDs) with high facet surface were chosen as the supported materials for studying the relation between the low loading amount of Pt atoms and the reaction mechanism of the HER activity. The atomic deposition of Pt atoms on the surface of Au NDs can be controlled effectively using a constant-current synthetic method. It was found that the HER electrocatalytic activity of ultralow Pt loading catalyst, with Pt atoms to total surface atoms of Au NDs (O-Pt on Au NDs) of 5.5%, could achieve high efficiency via the Tafel reaction pathway, showing a low overpotential of ∼18 mV at a current density of 10 mA cm−2 and a small Tafel slope of ∼31 mV dec−1, which is close to that of commercial Pt/C with 20 wt% Pt. As confirmed by Inductively Coupled Plasma Mass Spectrometry(ICP-MS), the Pt loading amount of O-Pt on Au NDs was ∼3.8 ± 0.2 μg cm−2 on a physical area of carbon fiber paper. The turnover frequency (TOF) of O-Pt on Au NDs was found to be 40.1 ± 2.5 H2 per s at 50 mV. This work provides a feasible approach to control the atomic deposition of Pt on a specific substrate as an active catalyst for various catalytic applications.

Binary transition-metal sulfide MnCo2S4 (MCS) and oxide MnCo2O4 (MCO) nanowires grown on nickel foam were prepared with facile hydrothermal method. The MCS electrode not only exhibits a large areal capacity, 1.17 mA h cm−2 at current density 3 mA cm−2 but also shows great rate capability and cycling stability in an alkaline electrolyte. In situ quick X-ray absorption spectroscopy of the Mn K-edge and Co K-edge of MCS demonstrate that both average valence states of elements Mn and Co show a notable change from the faradaic pseudocapacitance, inferring a synergistic effect of two elements. Based on a Co K-edge and Mn K-edge extended X-ray absorption fine structure analysis of MCS, some Mn–S/Co–S bonds on the surface of electrode are broken and then become active sites, which can react with hydroxide ions. Besides a synergistic effect of two elements, the active sites arising from the broken Mn–S/Co–S bonds hence enhance significantly the capacitive performance of the MCS electrode. Our work provides new insight into the electrochemical mechanism and the main difference for supercapacitor performance between MCS and the corresponding oxide MCO electrodes. These results demonstrate a different mechanism for binary transition metal sulfide and oxide in electrochemical reaction of energy storage.

We report temperature dependence of electrical conductivity and thermopower for poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films post-treated using a combination of an...

We demonstrate that the single-site catalyst Pt1/CeO2 greatly enhances the selectivity of cyclization and aromatization in the n-hexane reforming reaction. Specifically, the selectivity of single-site Pt1/CeO2 toward both cyclization and aromatization is above 86% at 350 °C. The turnover frequency of Pt1/CeO2 is 58.8 h-1 at 400 °C, which is close to that of Pt cluster/CeO2 (61.4 h-1) and much higher than that of Pt nanoparticle/CeO2 with Pt sizes of 2.5 and 7 nm. On the basis of the catalytic results for methylcyclopentane reforming, the dehydrocyclization and further aromatization of n-hexane are attributed to the prominent adsorption of ring intermediate products on the single-site Pt1/CeO2 catalysts. On the other side, with the multiple Pt adjacent active sites, the cluster and nanoparticle Pt/CeO2 samples favor the C-C bond cracking reaction. Ultimately, this in-depth study unravels the principles of hydrocarbon activation with different Pt sizes and represents a key step toward the rational design of new heterogeneous catalysts.

Palladium-catalysed oxidative carbonylation using oxygen as the oxidant is an economical approach; however, the gas mixture of CO and air has an explosive limit of 12.5–74.0% that could hamper extensive application of this process. Herein we report an electrochemical aminocarbonylation of alkynes under atmospheric pressure in an undivided cell without an external oxidant. The transformation has a broad substrate scope (83 examples) that involves primary amines and ammonium salts. Furthermore, mechanistic studies through cyclic voltammetry, in situ infrared and quick-scanning X-ray absorption fine structure spectroscopy reveal the reasons for this protocol proceeding smoothly under electrochemical conditions. Oxidative carbonylation using CO/O2 is an attractive strategy to construct carbonyl compounds, but the explosive limit of the gas mixture hampers its application. Now, this safety issue is overcome in the aminocarbonylation of alkynes by replacing the external oxidant O2 by electrochemistry facilitating a mild and safe reaction.