Activity For Oxidation Reaction Research Articles

Improving Alkaline Hydrogen Oxidation through Dynamic Lattice Hydrogen Migration in Pd@Pt Core-Shell Electrocatalysts.

Tracking the trajectory of hydrogen intermediates during hydrogen electro-catalysis is beneficial for designing synergetic multi-component catalysts with division of chemical labor. Herein, we demonstrate a novel dynamic lattice hydrogen (LH) migration mechanism that leads to two orders of magnitude increase in the alkaline hydrogen oxidation reaction (HOR) activity on Pd@Pt over pure Pd, even ≈31.8 times mass activity enhancement than commercial Pt. Specifically, the polarization-driven electrochemical hydrogenation process from Pd@Pt to PdHx @Pt by incorporating LH allows more surface vacancy Pt sites to increase the surface H coverage. The inverse dehydrogenation process makes PdHx as an H reservoir, providing LH migrates to the surface of Pt and participates in the HOR. Meanwhile, the formation of PdHx induces electronic effect, lowering the energy barrier of rate-determining Volmer step, thus resulting in the HOR kinetics on Pd@Pt being proportional to the LH concentration in the in situ formed PdHx @Pt. Moreover, this dynamic catalysis mechanism would open up the catalysts scope for hydrogen electro-catalysis.

Improving Alkaline Hydrogen Oxidation through Dynamic Lattice Hydrogen Migration in Pd@Pt Core‐Shell Electrocatalysts

AbstractTracking the trajectory of hydrogen intermediates during hydrogen electro‐catalysis is beneficial for designing synergetic multi‐component catalysts with division of chemical labor. Herein, we demonstrate a novel dynamic lattice hydrogen (LH) migration mechanism that leads to two orders of magnitude increase in the alkaline hydrogen oxidation reaction (HOR) activity on Pd@Pt over pure Pd, even ≈31.8 times mass activity enhancement than commercial Pt. Specifically, the polarization‐driven electrochemical hydrogenation process from Pd@Pt to PdHx@Pt by incorporating LH allows more surface vacancy Pt sites to increase the surface H coverage. The inverse dehydrogenation process makes PdHx as an H reservoir, providing LH migrates to the surface of Pt and participates in the HOR. Meanwhile, the formation of PdHx induces electronic effect, lowering the energy barrier of rate‐determining Volmer step, thus resulting in the HOR kinetics on Pd@Pt being proportional to the LH concentration in the in situ formed PdHx@Pt. Moreover, this dynamic catalysis mechanism would open up the catalysts scope for hydrogen electro‐catalysis.

In-situ synthesis of Cr2O3-enhanced bifunctionality in walnut-like Pt/CrN for methanol-assisted high-efficiency hydrogen generation

Methanol-assisted water electrolysis offers a promising alternative for low-voltage green hydrogen generation. Herein, we report the design and in-situ synthesis of Cr2O3, achieved by pyrolyzing a coordination polymer, to serve as cocatalysts. The Cr2O3 cocatalyst enhances the bifunctionality of the walnut-like Pt/CrN catalyst, leading to remarkable electrocatalytic activity in the methanol oxidation reaction (MOR) and hydrogen evolution reaction (HER) compared to Pt/CrN catalyst. Experimental data confirmed that Cr2O3 as a promoter accelerates the water dissociation, resulting in the formation of OHad. Additionally, it reduces the d-band center of Pt, favoring the optimization of the Gibbs free energy of intermediates. Moreover, the walnut-like Cr2O3–CrN facilitates mass diffusion and electron transfer. The synergistic effect between Cr2O3 and CrN, along with the presence of a hetero-interface, contributes to the enhancement of MOR/HER electrocatalytic activity. Thanks to these advantageous characteristics, the as-prepared Pt/Cr2O3–CrN catalysts exhibit superior MOR/HER performance, achieving a mass activity of 1.425 A mgPt−1 for MOR and an overpotential of 42 mV at a current density of 10 mA cm−2. Furthermore, with the Pt/Cr2O3–CrN as a bifunctional catalyst for both MOR and HER, the methanol-assisted electrolyzer only requires a cell voltage of 0.628 V to deliver a current density of 10 mA cm−2 for 10 h.

Diffusion-Restricted Cation Exchange Derived Rhodium Nanoparticles for Hydrazine Assisted Hydrogen Production

Water splitting using renewable energy is a promising hydrogen production method without carbon emission. However, oxygen evolution reaction still suffers from its large overpotential and sluggish kinetics. Thus, alternative oxidation reactions rather than oxygen evolution reaction, such as ammonia, alcohols and hydrazine oxidation reaction are developed for hydrogen production. Rh is one of the most promising catalysts for electrochemical hydrazine splitting that can promote hydrogen evolution reaction on the cathode, which is a much more energy-saving way to generate hydrogen gas than water splitting. Unfortunately, Rh is also one of the most expensive novel metals on the market. Nevertheless, only a few studies have considered the amount of used Rh. In this study, the diffusion-restricted cation exchange (CE) process is suggested as an effective method to reduce the mass of inactive Rh for enhanced mass activity. By immersing the NiOOH substrate in the Rh3+ aqueous solution, Rh3+ atoms are easily exchanged with Ni3+ atoms in the NiOOH lattice on the surface, and the RhOOH forms on the outermost layer. Then, the RhOOH compounds are reduced into metallic rhodium by an electrochemical reduction process, resulting in fine Rh nanoparticles smaller than 2 nm. Due to the suppression of Rh aggregation, a doubled mass activity for electrocatalytic hydrazine oxidation reaction is attained compared to that of conventional electrodeposited Rh catalysts. As a result, the proposed CE-derived Rh catalyst shows stability over 36 hours under the two-electrode hydrazine splitting system.

Fabrication of Self-Standing Porous Foam-like PdM (M = Ni, Fe, Co) Nanocrystals for Boosted Ethanol Oxidation Electrocatalysis

Rational designing of self-standing porous foam-like PdM (M = Ni, Fe and Co) nanocrystals was achieved by a fast aqueous-solution method via the co-reduction of metal precursors using sodium borohydride. This was based on the crystallites’ coalescence growth mechanism, including quick nucleation of Pd that served as starting seeds for the nucleation of M, which attached directly along the specific crystallographic and lowered its high surface energy by diffusion of PdM atoms across the interface via Brownian motion to afford self-standing porous foam-like PdM nanocrystals. Amongst the as-prepared PdM nanocrystals, PdNi nanocrystals showed a superior alkaline ethanol oxidation reaction (EOR) activity and stability compared to PdFe, PdCo, Pd nanospheres (Pd-NSs) and commercial Pd/C (10 wt.%) catalysts. The EOR mass activity of PdNi was 1.32, 1.51, 2.01 and 24.05 times than those of PdFe, PdCo, Pd-NSs and Pd/C, respectively based on equal Pd mass. This was attributed to the lower synergistic effect in PdNi, which enhanced H2O activation/dissociation to give OH- species needed for rapid EOR kinetics, meanwhile, the porous foam-like morphology improved electron mobility and increased accessible active sites. This study revealed that low synergism in porous PdM nanocrystals is beneficial for enhancing the EOR activity and durability, which may allow the design of other binary Pd-based alloys for various electrocatalytic reactions.

Development of IrO2 Nanosheet–Pt/C Composite as Reversal Tolerant Anode Catalysts for Polymer Electrolyte Fuel Cell

Introduction: During the start-up and shutdown cycles of a polymer electrolyte fuel cell (PEFC), certain areas of the anode flow channel may not receive sufficient hydrogen due to water blockage or sluggish diffusion. This can lead to hydrogen starvation, which in turn causes a shortage of protons during cell reaction. The result is an increase in anode potential, which triggers the carbon oxidation reaction (COR) and damages the catalyst layer.Promoting the oxygen evolution reaction (OER) to alleviate the COR is a promising strategy to develop reversal-tolerant anodes (RTAs). Incorporating OER-active materials, such as IrO2, as a co-catalyst is an effective way to mitigate the rise in anode potential and prevent COR [1].In this study, a novel OER-active material, iridium oxide nanosheet (IrO2(ns)), was used as the co-catalysts and combined with commercial Pt/C in three different ways; mixing Pt/C with normal- and small-sized IrO2 nanosheets (IrO2(ns)/Pt/C), and Pt/C mixed with carbon supported IrO2 nanosheet (Pt/C+IrO2(ns)/KB). The OER activity and tolerance to cell reversal conditions were characterized using a 3-electrode rotating disk electrode (RDE) setup. Experiment: IrO2(ns)(250 nm) colloid was synthesized following literature [2]. The resulting IrO2(ns)(250 nm) colloid was subjected to ultrasonication to obtain small-sized nanosheets (IrO2(ns)(100 nm)) [3]. Nanosheet-carbon composite (IrO2(ns)(100 nm)/KB) was prepared by mixing IrO2(ns)(100 nm) colloid and KB (Ketjen black EC-300J) and physically mixed with Pt/C. Commercially available IrO2 nanoparticles (c-IrO2) were purchased from Tokuriki Honten Co., Ltd. and added to Pt/C (c-IrO2-Pt/C) and used as a reference sample.The composite catalyst was prepared by mixing Pt/C with different IrO2 nanomaterials and will be denoted as IrO2(ns)(x mass%)-Pt/C or c-IrO2 (x mass%)-Pt/C depending on the source of the IrO2 material used. RDE studies were conducted using a 3-electrode half-cell setup with 0.1 M HClO4 as the electrolyte. The counter electrode was carbon fiber, and a reversible hydrogen electrode (RHE) was used as the reference electrode.Except for the OER activity, the electrodes for all measurement were prepared with a Pt loading of 8.0 μg/cm2. For hydrogen oxidation reaction (HOR) activity measurements, the electrolyte was purged with H2. For chronopotentiometry (CP) and electrochemically active Pt surface area (ECSA) measurement, the electrolyte was purged with N2. For OER activity measurements, the electrolyte was purged with N2, and the working electrode was prepared with a Pt loading of 17.3 μg/cm2. Except for ECSA measurement, all data were accumulated at an electrolyte temperature of 60oC. Results and Discussion: Figure 1 shows the OER activity (10 mV/s) of Pt/C and composite catalysts prepared with c-IrO2(5 mass%), IrO2(ns)(250 nm, 5 mass%), IrO2(ns)(100 nm, 5 mass%), IrO2(ns)(100 nm, 2.5 mass%) and IrO2(ns)(100 nm, 1 mass%). At 1.5 V vs. RHE, IrO2(ns)(100 nm, 2.5 mass%)-Pt/C exhibited a 2-fold increase in OER activity compared to IrO2(ns)(250 nm, 5 mass%)-Pt/C and a 25 % increase compared to c-IrO2 (5 mass%)-Pt/C. All composite catalysts displayed significantly higher OER activity than the pristine Pt/C sample.To simulate the degradation behavior in the fuel cell anode, a series of CP tests were performed at 16, 48, 80, and 112 μA/cm2. The HOR mass activity was used as a quantitative factor to present the decay caused by cell reversal degradation. The HOR activity before and after CP was evaluated using linear sweep voltammetry (LSV) from -0.08 V to 0.5 V vs. RHE. The HOR mass activity at 20 mV vs. RHE was calculated based on the Koutecky-Levich equation. After CP, the Pt/C sample showed a decrease in HOR activity from 851 A/g to 621 A/g (72% retention). In contrast, IrO2(ns)(100 nm, 2.5 mass%)-Pt/C showed an initial HOR activity comparable to Pt/C (1420 A/g) and still retained a high HOR activity of 1400 A/g after CP (100% retention). The addition of IrO2(ns) as a co-catalyst effectively suppressed the carbon oxidation reaction under cell reversal conditions.

NiFe sulfide electronic structure modulation via metal doping towards enhanced urea oxidation reaction performance

Enhancement of urea oxidation reaction (UOR) activity of NiFe sulfide via metal doping, including V, Zn, Cr, Ag, and Ti, is demonstrated. X-ray photoelectron and absorption spectroscopy analyses show different degrees of electronic structure modulation of the Ni site due to the doping of the third metals having different t2g and eg occupancies. Cr reduces the energy needed for the in-situ formation of the oxyhydroxide, followed by Ti, V, and Ag. The reaction kinetics is accelerated by Ti, followed by Ag, Cr, and Zn. Ti also optimizes the d-band center and CO2 adsorption energy, which is supported by density functional theory calculation. Self-reconstructed sulfate-containing oxyhydroxide during UOR is demonstrated via in-situ Raman and post-transmission electron microscopy analyses. The sulfate is also found to affect the potential required for the formation of the oxyhydroxide. The optimized NiFeTi-containing sulfide exhibits an excellent UOR potential of 1.36 V at 100 mA cm−2 and is stable up to 80-h. This work provides a strategy and deep understanding in enhancing UOR performance of sulfide catalyst.

Zirconium (Oxy)Nitrides for (Photo)Electrochemical Applications

Transition metal (TM) nitrides are an emerging class of (photo)electrocatalytic materials that have recently received growing research interest.1,2 In general, nitrogen-poor TM nitrides are usually refractory materials with metallic character while nitrogen-rich nitrides often possess semiconducting character.3 Hence, while the former are potential electrocatalyst candidates, the latter may qualify as photoelectrode absorber materials. For example, ZrN has recently been proposed as an electrocatalyst for both the electrochemical nitrogen4 and oxygen5 reduction reactions (ORR and NRR), while Zr3N4 and also Zr2N2O have been suggested as potential photoanode materials in photoelectrochemical water oxidation.2 In this contribution, we test these hypotheses regarding the (photo)electrochemical characteristics of Zr-based (oxy)nitrides by experiment. To this end, we investigate reactively sputtered thin films for the electrochemical NRR/ORR and the photoelectrochemical oxygen evolution reaction (OER). Previous experiments on Ta-based nitrides have shown that addition of oxygen during the reactive sputter process is necessary to access higher metal oxidation states.6 As we introduce controlled amounts of oxygen at otherwise fixed deposition conditions, we observe a transition from metallic ZrN to a disordered nitrogen-rich ZrxNy to a crystalline bixbyite-type Zr2N2O to nitrogen-doped cubic ZrO2. Crystalline Zr3N4 was not accessible under the used experimental conditions. In our experiments, we observe a lack of electrocatalytic activity for ZrN in NRR and ORR and instabilities of the disordered nitrogen-rich ZrxNy in the photoelectrochemical OER. Introducing more oxygen into the structure, however, leads to a more stable crystalline structure (Zr2N2O), the opening of a band gap in the visible range, and the emergence of photoelectrochemical activity for oxidation reactions. Based on chopped linear sweep voltammetry measurements, we show that Zr2N2O films are photoactive for the OER in alkaline electrolyte with low onset potentials, indicating an overall favorable band alignment of the material with respect to the water oxidation and reduction potentials. While the observed photocurrents are still about one order of magnitude lower than for the benchmark oxynitride photoanode TaON, further material optimization could potentially close this gap and provide a materials system functioning as sustainable photoanode.References 1 W. Sun, C.J. Bartel, E. Arca, S.R. Bauers, B. Matthews, B. Orvañanos, B.R. Chen, M.F. Toney, L.T. Schelhas, W. Tumas, J. Tate, A. Zakutayev, S. Lany, A.M. Holder, and G. Ceder, Nat. Mater. 18, 732 (2019). 2 Y. Wu, P. Lazic, G. Hautier, K. Persson, and G. Ceder, Energy Environ. Sci. 6, 157 (2013). 3 A. Salamat, A.L. Hector, P. Kroll, and P.F. McMillan, Coord. Chem. Rev. 257, 2063 (2013). 4 Y. Abghoui, A.L. Garden, J.G. Howalt, T. Vegge, and E. Skúlason, ACS Catal. 6, 635 (2016). 5 Y. Yuan, J. Wang, S. Adimi, H. Shen, T. Thomas, R. Ma, J.P. Attfield, and M. Yang, Nat. Mater. 19, (2019). 6 C.M. Jiang, L.I. Wagner, M.K. Horton, J. Eichhorn, T. Rieth, V.F. Kunzelmann, M. Kraut, Y. Li, K.A. Persson, and I.D. Sharp, Mater. Horizons 8, 1744 (2021).

The Trade-Off Relationship between Particle Proximity Effect and Low-Pt Loading to Optimize Oxygen Reduction and Methanol Oxidation Reaction Activity

Pt-based electrocatalysts have long been considered as the most effective oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) catalysts due to their excellent intrinsic activity. For supported catalysts, Pt loading, particle size, interparticle distance (ipd), and interaction with support are identified as key contributors for high activity and selectivity. The proximity effect is a relatively new topic in catalysis research. There is a contradiction between the traditional view which induces the electronic interaction to reduce the activity and the new view which causes the electrical double-layer overlap of adjacent nanoclusters, changes the potential distribution and improves the specific activity. [1, 2]To this end, we have developed the nitrogen-doped graphite-like carbon sheets supporting low-Pt loading (Pt@N-GC) with uniform sizes and controllable ipd, and disentangled the main effect of ipd on ORR activity/selectivity and MOR activity/CO tolerance. Combining electrochemical tests and the trade-off mechanism between proximity effect and low-Pt loading, the following trends were obtained:1) 10.0 wt% Pt@N-GC with highest Pt loading and lowest ipd inhibits 2e- ORR by strong adsorption and reabsorption of *OOH due to the presence of closer Pt sites, and improves 4e- ORR selectivity. However, the mass activity/specific activity reached the maximum under the optimal low-Pt loading of 5.0 wt%.2) Similarly, 10.0 wt% Pt@N-GC weakened the adsorption of the -OH group of oxidized COads intermediates, led to the strong adsorption of COads on the catalyst surface, inactivated of Pt sites and reduced the CO resistance. Considering the need to improve CO tolerance while increasing MOR activity, the 5.0 wt% low-Pt loading catalyst exhibiting the best MOR performance under the optimal ipd.3) Benefiting by the synergistic effect of Pt nanoparticles and N-GC support, all Pt@N-GCs exhibit bifunctional electrocatalytic activity and durability.We attribute these findings to the underlying mechanism trade-off between the particle proximity effect and low-Pt loading under the uniform particle size and controlled ipd (Figure. 1). We believe the proximity effect has positive and negative effects, how to maximize the advantages of proximity effect can provide valuable guidance for the design and optimization of low-Pt loading bifunctional electrocatalysts in the future.[1] M. Nesselberger, M. Roefzaad, R.F. Hamou, P.U. Biedermann, F.F. Schweinberger, S. Kunz, K. Schloegl, G.K. Wiberg, S. Ashton, U. Heiz, K.J. Mayrhofer, M. Arenz, Nat. Mater., 12 (2013) 919-924.[2] M. Watanabe, H. Sei, P. Stonehart, J. Eelectroanal. Chem., 261 (1989) 375-387. Figure 1. The trade-off mechanism analysis between proximity effect and low-Pt loading. Figure 1

Epitaxial Ultrathin Pt Atomic Layers on CrN Nanoparticle Catalysts.

The construction of platinum (Pt) atomic layers is an effective strategy to improve the utilization efficiency of Pt atoms in electrocatalysis, thus is important for reducing the capital costs of a wide range of energy storage and conversion devices. However, the substrates used to grow Pt atomic layers are largely limited to noble metals and their alloys, which is not conducive to reducing catalyst costs. Herein, low-cost chromium nitride (CrN) is utilized as a support for the loading of epitaxial ultrathin Pt atomic layers via a simple thermal ammonolysis method. Owing to the strong anchoring and electronic regulation of Pt atomic layers by CrN, the obtained Pt atomic layerscatalyst (containing electron-deficient Pt sites) exhibits excellent activity and endurance for the formic acid oxidation reaction, with a mass activity of 5.17AmgPt -1 that is 13.6 times higher than that of commercial Pt/C catalyst. This novel strategy demonstrates that CrN can replace noble metals as a low-cost substrate for constructing Pt atomic layers catalysts.

Flower-like WO2@C prepared from the pyrolyzation of ionic liquid for effective elctrocatalytic two-electron water oxidation

Flower-like tungsten dioxide@carbon (WO2@C) is prepared through the pyrolysis of 1-octyl-3-methylimidazolium tungstate ionic liquids. The resultant WO2 particles are surrounded by a few of carbon fibers, displaying the unique flower-like morphology. The WO2@C testified efficient electrocatalytic activity for two-electron water oxidation reaction (2e- WOR) to H2O2. The electrocatalytic H2O2 production rate reaches about 6.55 μmol min−1 cm−2, over 2 times higher than WO2. This may be ascribed to the enhanced electron transferring capacities and abundant defects of WO2@C. This work introduces a special ionic liquid-derived metal oxide@C with the improved electrocatalytic activity for 2e- WOR.

Construction of ultrathin PdPtSn nanosheet for alcohol oxidation reaction

Pd-based nanosheets are potential catalysts for direct alcohol fuel cells since their abundant active sites and huge specific areas. Because of the special properties of nanosheets, enormous efforts have been paid to explore excellent performance Pd-based nanosheets. There is still a great challenge to synthesize novel nanosheets for alcohol oxidation. Here, we develop a low-temperature seed-oriented approach to synthesize Pd-based nanosheets by a two-step method. The produced PdPtSn nanosheets inherit the morphology of Pd nanosheets but dramatically increase electrochemistry activity, which could be attributed to the synergistic effect among Pd, Pt, and Sn. The ultrathin PdPtSn NSs own a huge surface and high electrical conductivity that perform catalytic activity at 4.1 A mgPd−1 for methanol oxidation far beyond commercial Pd/C. Meanwhile, PdPtSn NSs keep 0.82 A mgPd−1 after 500 cycles in alkaline environment for methanol oxidaton, which is attributed to the modified electronic structure of the Pd by the addition of Pt and Sn. The prepared PdPtSn NSs also perform high catalytic activity for glycol oxidation reaction with 16.2 A mgPd−1 which is about 20 times more than that of commercial Pd/C. This work provides a new strategy to make Pd-based nanosheets for highly efficient MOR electrocatalysts.

Tuning the Cerium-Based Metal-Organic Framework Formation by Template Effect and Precursor Selection.

The novel metal-organic framework [(CH3)2NH2]2[Ce2(bdc)4(DMF)2]·2H2O (Ce-MOF, H2bdc-terephthalic acid, DMF-N,N-dimethylformamide) was synthesized by a simple solvothermal method. Ce-MOF has 3D connectivity of bcu type with a dinuclear fragment connected with eight neighbors, while three types of guest species are residing in its pores: water, DMF, and dimethylammonium cations. Dimethylamine was demonstrated to have a decisive templating effect on the formation of Ce-MOF, as its deliberate addition to the solvothermal reaction allows the reproducible synthesis of the new framework. Otherwise, the previously reported MOF Ce5(bdc)7.5(DMF)4 (Ce5) or its composite with nano-CeO2 (CeO2@Ce5) was obtained. Various Ce carboxylate precursors and synthetic conditions were explored to evidence the major stability of Ce-MOF and Ce5 within the Ce carboxylate-H2bdc-DMF system. The choice of precursor impacts the surface area of Ce-MOF and thus its reactivity in an oxidative atmosphere. The in situ PXRD and TG-DTA-MS study of Ce-MOF in a nonoxidative atmosphere demonstrates that it eliminates H2O and DMF along with (CH3)2NH guest species in two distinct stages at 70 and 250 °C, respectively, yielding [Ce2(bdc)3(H2bdc)]. The H2bdc molecule is removed at 350 °C with the formation of novel modification of Ce2(bdc)3, which is stable at least up to 450 °C. According to the total X-ray scattering study with pair distribution function analysis, the most pronounced local structure transformation occurs upon departure of DMF and (CH3)2NH guest species, which is in line with the in situ PXRD experiment. In an oxidative atmosphere, Ce-MOF undergoes combustion to CeO2 at a temperature as low as 390 °C. MOF-derived CeO2 from Ce-MOF, Ce5, and CeO2@Ce5 exhibits catalytic activity in the CO oxidation reaction.

Modulating Electronic Structure and Atomic Insights into the Novel Hierarchically Porous PdCuFe Trimetallic Alloy Aerogel for Efficient Oxygen Reduction.

The high cost of noble Pd/Pt required for the oxygen reduction reaction (ORR) in the cathode restricts the wide applications of fuel cells. In this study, the synthesis of a novel Pd3CuFe0.5 aerogel electrocatalyst is successfully demonstrated using self-assembly and lyophilization techniques, employing a mild reducing agent. The resulting aerogel electrocatalyst exhibits a distinctive 3D network structure, possessing a substantial BET-specific surface area of 75.19 m2g-1. It is worth noting that the optimized Pd3CuFe0.5 aerogel demonstrates exceptional ORR performance with a high half-wave potential of 0.92V versus RHE, a significant limiting current density of 7.6mAcm-2, and the excellent electrocatalytic stability, superior to the reported noble metal electrocatalysts, with the ORR activity decays only 4.9% after 16000 s. In addition, the Pd3CuFe0.5 aerogel electrocatalyst shows superior cycling stability for ≈120h at a charge/discharge current density of 10mAcm-2, indicating its promising application in fuel cells. Furthermore, the resulting composite aerogel possesses excellent hydrogen evolution reaction and ethanol oxidation reaction activity. The density functional theory calculations show that the partial oxidation of Pd3CuFe0.5 aerogel leads to a negative shift of the d-band center, which energetically optimizes the binding strength of *O intermediates, therefore accelerating the ORR activity.

Crown-hydroxylamines are pH-dependent chelating N,O-ligands with a potential for aerobic oxidation catalysis

Despite the rich coordination chemistry, hydroxylamines are rarely used as ligands for transition metal coordination compounds. This is partially because of the instability of these complexes that undergo decomposition, disproportionation and oxidation processes involving the hydroxylamine motif. Here, we design macrocyclic poly-N-hydroxylamines (crown-hydroxylamines) that form complexes containing a d-metal ion (Cu(II), Ni(II), Mn(II), and Zn(II)) coordinated by multiple (up to six) hydroxylamine fragments. The stability of these complexes is likely to be due to a macrocycle effect and strong intramolecular H-bonding interactions between the N−OH groups. Crown-hydroxylamine complexes exhibit interesting pH-dependent behavior where the efficiency of metal binding increases upon deprotonation of the hydroxylamine groups. Copper complexes exhibit catalytic activity in aerobic oxidation reactions under ambient conditions, whereas the corresponding complexes with macrocyclic polyamines show poor or no activity. Our results show that crown-hydroxylamines display anomalous structural features and chemical behavior with respect to both organic hydroxylamines and polyaza-crowns.

Oxygen vacancies modulated Co3O4 toward highly efficient electrooxidation of 5-hydroxymethylfurfural

Electrochemical oxidation of 5-hydroxymethylfurfural (HMF) has emerged as a promising method to produce highly valuable chemicals. Co-based electrocatalysts with oxygen vacancies are one of the most promising candidates. However, the relationship between their electrocatalytic behavior and the vacancy concentration is still ambiguous. In this work, the diverse oxygen vacancy contents of Co3O4 were realized via a simple adsorption-pyrolysis method and confirmed by X-ray diffraction, Raman, transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, respectively. It was found that the Co3O4 with proper oxygen vacancies prepared at optimized conditions exhibits a superior catalytic activity for HMF oxidation reaction (HMFOR) in 1.0 M KOH with 50 mM HMF electrolyte (with the potential of 1.35 V vs. RHE at 10 mA cm−2). Correlational characterizations and density functional theory calculations demonstrate that appropriate oxygen vacancies can promote HMF electrooxidation performance, whereas excessive oxygen vacancies can hinder electron transport and result in a significant decline in HMF electrooxidation performance. This study reveals the significance of appropriate oxygen vacancies in catalytic oxidation activity and provides important insights into the role of oxygen vacancies in catalytic oxidation reactions for the synthesis of defective material.

Enhanced Activity of Small Pt Nanoparticles Decorated with High-Loading Single Fe─N4 for Methanol Oxidation and Oxygen Reduction via the Assistive Active Sites Strategy.

Decorating platinum (Pt) with a single atom offers a promising approach to tailoring their catalytic activity. In this study, for the first time, an innovative assistive active sites (AAS) strategy is proposed to construct high-loading (3.46wt.%) single Fe─N4 as AAS, which are further hybridized with small Pt nanoparticles to enhance both oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activities. For ORR, the target catalyst (Pt/HFeSA-HCS) exhibits a higher mass activity (MA) of 0.98AmgPt -1 and specific activity (SA) of 1.39mAcmPt -2 at 0.90V versus RHE. As for MOR, Pt/HFeSA-HCS shows exceptional MA (3.21AmgPt -1) and SA (4.27mAcmPt -2) at peak values, surpassing commercial Pt/C by 15.3 and 11.5 times, respectively. The underlying mechanism behind this AAS strategy is to find that in MOR, Fe─N4 promotes water dissociation, generating more *OH to accelerate the conversion of *CO to CO2. Meanwhile, in ORR, Fe─N4 acts as a competitor to adsorb *OH, weakening Pt─OH bonding and facilitating desorption of *OH on the Pt surface. Constructing AAS that can enhance dual functionality simultaneously can be seen as a successful "kill two birds with one stone" strategy.

Amorphous-crystalline heterostructure: Efficient catalyst for biomass oxidation coupled with hydrogen evolution

The development of catalysts with high activity, selectivity, and stability is critical for biomass upgrading coupled with hydrogen evolution. In this study, we present a simple method for fabricating crystalline-amorphous phase heterostructures using the etching effect of the acidic medium generated during cobalt salt hydrolysis, resulting in the formation of NiCo(OH)x-modified Ni/NiMoO4 nanosheets electrode (NiCo(OH)x/Ni/NiMoO4/NF). The nanosheets array formed during the synthesis process enlarges the surface area of the prepared catalyst, which facilitates the exposure of electrochemically active sites and improves mass transfer. Unexpectedly, the strong coupling interactions between the amorphous-crystalline heterointerface optimize the adsorption of reaction molecules and the corresponding charge transfer process, consequently boosting the catalytic activity for the 5-hydroxymethylfurfural oxidation reaction (HMFOR) and hydrogen evolution reaction (HER). Specifically, NiCo(OH)x/Ni/NiMoO4/NF catalyst requires only 1.34 V to obtain a current density of 10 mA cm−2 for HMFOR-coupled H2 evolution, and operates stably for 13 consecutive cycles with good product selectivity. This work thus provides insights into the design of efficient and robust catalysts for HMFOR-assisted H2 evolution.

Ultrathin Co0.5NiS Nanosheets for Hydrazine Oxidation Assisted Nitrite Reduction

AbstractNitrite (NO2−) and hydrazine (N2H4) are common N‐pollutants in groundwater. The electrochemical method can realize the treatment of N‐pollutants and the synthesis of energy substance ammonia (NH3). Designing and synthesizing efficient electrocatalysts is of great significance. Herein, ultrathin Co0.5NiS nanosheets attached on nickel foam (Co0.5NiS‐NSs/NF) are synthesized via cyanogel‐NaBH4 hydrolysis process and succedent sulfurization approach. Owing to the ultrathin nanosheet structure and the interaction between Ni and Co, Co0.5NiS‐NSs/NF exhibits high activity for NO2− reduction reaction (NO2−RR), in which the Faraday efficiency is 92.2% and the NH3 yield is 0.25 mmol h−1 cm−2 at −0.15 V potential. Meanwhile, Co0.5NiS‐NSs/NF also displays remarkable activity for N2H4 oxidation reaction in KOH electrolyte. Therefore, a symmetrical Co0.5NiS‐NSs/NF||Co0.5NiS‐NSs/NF electrolyzer is assembled, which only needs the operating voltage of 0.36 V to reach 10 mA cm−2 for NO2−‐to‐NH3 conversion in the presence of N2H4. This work reports a promising and efficient strategy for NH3 production at a small operating voltage and treatment of the N‐pollutants.

SAXS Application for the Determination of the Gold Nanoparticle Sizes in Au/C Catalysts: Advantages over Other Methods

In the case of Au/C catalysts have been shown advantages of application SAXS with masking liquid technique for determining supported metal particle sizes compared with TEM and XRD as standard methods. According to SAXS data particle size distributions of gold in a wide range (1–50 nm) were obtained with full consideration of all size fractions of particles present in the samples under study. Also values of the mass fraction of “X-ray amorphous” gold particles with size less than 4 nm (WSAXS) were determined. It has been found that the oxidative treatment of the carbon support before deposition of metallic gold precursor complexes has a significant effect on the size distribution of gold particles in the final catalyst. Comparison of the results of measuring the rate of CO oxidation by an excess of moist air at 40°C on Au/C catalysts with the (WSAXS) values found for these catalysts showed that the catalytic activity increases exponentially as (WSAXS) increases. High activity in CO oxidation reaction was demonstrated by Au/C catalysts with (WSAXS) ≥ 80%.