查看更多>>摘要：? 2022 Elsevier B.V.Oxygen evolution reaction (OER) is a key step for electrochemical water splitting and understanding the surface reconstruction of OER pre-catalysts is of vital importance. Herein, hybrid Ni5P4 @FeP nanosheet arrays were evaluated as promising OER pre-catalysts. The dynamic surface evolution was probed by in situ Raman spectroscopy, which revealed that Ni5P4 @FeP was rapidly reconstructed to NiFe2O4 during the anodic scan. The structural instability of amorphous NiFe2O4 led to partial reconstitution to Ni/FeOOH at high oxidation potentials. As-formed Ni/FeOOH@NiFe2O4 hybrid with high structural reversibility was established as a truly active species, which exhibited excellent alkaline OER performance with a low overpotential of 205 and 242 mV under current densities of 10 and 100 mA cm?2, respectively. This work provides a facile strategy to in situ construct an amorphous spinel/oxyhydroxide hybrid structure using electrochemical activation that holds strong promise for potential application in electrochemical water splitting and related energy devices.
查看更多>>摘要：? 2021 Elsevier B.V.Developing the high-performance intermetallic bi–metal boride OER catalysts with a high density of grain boundaries and appropriate electronic structure is still a challenge. Herein, we synthesized an intermetallic (FexCo1?x)2B OER catalyst (GB-(FexCo1?x)2B) with controllable grain boundary densities by a facile ball-milling method. Benefiting from the modulation of both grain boundary density and electronic structure, the GB-(Fe0.66Co0.34)2B supported on reduced graphene oxide shows a low OER overpotential of 221 mV at a current density of 10 mA cm?2 and Tafel slope of 38.2 mV dec?1. The experimental and theoretical calculated methods demonstrate that the Fe introduction into the intermetallic Co2B catalyst can produce the higher grain boundary density and modulate the electronic structure, respectively. This work provides a promising insight in understanding the synergetic effects in bimetallic for GB-(FexCo1?x)2B systems and supports a new strategy to explore other efficient catalysts with a high density of grain boundaries.
查看更多>>摘要：? 2022 Elsevier B.V.Due to highly heterogeneity of pyrolyzed transition metal-nitrogen-carbon (M-N-C) catalyst, elucidating mechanisms of roles of metal in enhancing oxygen reduction reaction (ORR) is challenging. Here, we design a surface structurally-defined precursor with Fe-N coordination to atomically disperse iron (Fe) on N-doped carbon hollow microspheres surface (NHMs@Fe) by pyrolysis of the precursor. The obtained NHMs@Fe catalyst exhibits a high ORR activity comparable to commercial Pt/C catalyst. The detailed analyses confirmed that (i) Fe atoms are uniformly distributed on N-poor carbon surface, and (ii) the designed Fe-Nx coordination are destroyed and don't convert into Fe-Nx active sites after thermal activation. We find that single Fe atoms produced by carbothermal reduction are directly trapped into adjacent carbon vacancies generated by the removal of N to create active sites for ORR. This work not only reveals the origin of activity of Fe-N-C catalyst but also opens an avenue for preparation of high-performance M-N-C catalysts.
查看更多>>摘要：? 2021 Elsevier B.V.Electrochemical production of H2O2 from O2 via the two-electron reaction pathway (2e-ORR) is a promising alternative to the energy- and organic pollutant-intensive industrial anthraquinone process. However, irrespective of numerous research efforts on catalyst design and remarkable advances made in this area, the catalysts displaying high H2O2 production rate so far unexceptionally required expensive/hazardous catalyst precursors and involved tedious steps and/or harsh treating conditions. Herein, we report a slightly nitrogen-doped carbon 2e-ORR catalyst that was synthesized simply by pyrolyzing a polydopamine (PDA) coating on Vulcan XC72 carbon black (p-PDA/XC). In H2O2 production via ORR in an acidic electrolyte, the catalyst showed 185 mV less overpotential than XC and remarkably high selectivity up to 96%. Highly efficient and durable H2O2 production was demonstrated by the stable accumulation of H2O2 to 1368 mmol gcat?1 within 8 h, translating to a H2O2 production rate of 171 mmol gcat?1 h?1. A good linear relationship was identified between the H2O2 partial current and the surface content of the C–O/C–N and C[dbnd]O species for the XC and p-PDA/XC catalysts, inferring that the C atoms in or adjacent to these species serve as the active sites for 2e-ORR to H2O2. The inexpensive starting materials, facile synthetic strategy, and excellent catalytic performance of the p-PDA/XC catalyst may accelerate the establishment of an affordable, safe, and direct O2-to-H2O2 electrochemical process.
查看更多>>摘要：? 2021 Elsevier B.V.Electron paramagnetic resonance, in situ diffuse reflection infrared Fourier transform spectroscopy, and temperature-programmed techniques by means of the isotopic trace strategies were used to investigate the effects of water vapor on oxygen species, reaction pathways, byproducts distributions, and accumulation of the chlorine and carbon species on the catalyst surface for 1,2-dichloroethane oxidation over Ru/WO3 or Ru/TiO2 catalyst. The introduction of water vapor produced the OOH species that were converted into more active oxygen (O2– and O?) species. The mulliken population analysis indicates that βC and αC in VC are bonded with H and nucleophilic oxygen of ?OH in sequence, respectively, which proved that water directly promoted the transformation of vinyl chloride to CH3COOH. Besides, water could be partially adsorbed at the hydroxyl groups on the Ru/WO3 sample surface, which were provided the adsorption sites for 1,2-dichloroethane molecules. However, the severe competitive adsorption on the surface of Ru/TiO2 resulted in insufficient oxygen adsorption to supplement the oxygen vacancy.
查看更多>>摘要：? 2021 Elsevier B.V.Pt/CeO2 has gained much attention for their high activity in low-temperature (LT) water-gas shift (WGS) reaction. However, the inclusion of H2 in the feed as in the practical reaction condition significantly degrades the LT-WGS activity of the Pt/CeO2 catalysts. In this contribution, the activity of Pt/CeO2 catalyst under the feed gas containing excess H2 (20 vol% of H2) was enhanced more than three times by forming CeO2 nano-patches on Pt nano-particles. Both in-situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculation results indicate that dissociated H2 on the Pt nano-particle inhibits the activity of the Pt/CeO2 catalysts by occupying the active sites (Pt nano-particle-CeO2 interface). On the other hand, thin CeO2 nano-patches on Pt nano-particle suppressed the H2 dissociation. As a result, the WGS reactivity of the active Pt nano-particle-CeO2 interface was less affected by H2, granting the catalysts the high activity under the practical reaction conditions.
查看更多>>摘要：? 2021 Elsevier B.V.Bi/BiOCl/Bi2O2CO3 heterojunction was prepared via one-step hydrothermal process under the synergistic catalysis of Ni2+, where Bi(NO3)3 was employed as Bi source, DMF was used as carbon source and reductant, NiCl2 was adopted as Cl source and co-catalyst. The content of Bi, BiOCl and Bi2O2CO3 can be adjusted by changing the reaction time, temperature, content of DMF and NiCl2. The doping of Bi enhanced the photocatalytic activity of BiOCl/Bi2O2CO3 under visible-light. Bi/BiOCl/Bi2O2CO3 presented photo-degradation activity for environmental pollutants of rhodamine B, sunset yellow and tetracycline, which were 13.01, 9.40, 1.50 times and 168.38, 10.90, 4.75 times higher than BiOCl and Bi2O2CO3, respectively. The improved photocatalytic activity was ascribed to the sensitized effect of Bi and BiOCl, the surface plasmon resonance effect and the heterojunction structure, which inhibited the recombination of photogenerated electron-hole pairs. The degradation mechanism for rhodamine B was discussed, and the decreased toxicity of the degradation products was demonstrated.
查看更多>>摘要：? 2021 Elsevier B.V.The reasonable design of porous structures is important but usually overlooked for nonprecious metal ORR catalysts. In this study, a facile dual melt-salt-mediated templating method is developed to prepare a Fe-N-C catalyst with tailored porous framework. The ZnCl2 and NaCl are employed to construct abundant micropores and promote the transformation of partial micropores to mesopores, respectively, reasonably forming a 3D hierarchically porous framework. The catalyst demonstrates a satisfactory surface area (1605 m2/g), promoting mass transport and exposure of FeN4 sites. Interestingly, the dual melt-salt templates avoid rapid loss of nitrogen during pyrolysis, thus enhancing Fe-N4 active center density. Therefore, the obtained Fe-N-C material presents outstanding ORR performance in both alkaline and acid media, as well as good stability. The advances of this catalyst are further proved in liquid and solid-state Zn-air battery, with nice discharge stability and high peak power densities.
查看更多>>摘要：? 2022 Elsevier B.V.Owing to their high CO2 methanation activity, the direct hydrogenation of CO2 to long-chain C5+ over Co-based catalysts is challenging. Here, we demonstrate a Na- and Mn-promoted, core-shell Co@CoOx/Co2C catalyst that produces a high C5+ yield of 21.1% at a CO2 conversion of 64.3% and low temperature of 270 °C. CO2 conversion and C5+ selectivity are ensured during long-term catalytic reactions up to 1425 h. C21+ selectivity increases to 14.9% with increasing time on stream. The catalyst exhibits high C5+ and C21+ selectivity, making it a promising option for producing liquid fuels and lube base oil in one-pass CO2 conversion. Direct CO2 dissociation and formate formation over the oxygen-vacant Co3O4 phase in the shell is the plausible reverse–water–gas–shift reaction mechanism. The Mn promoter facilitates the formation of the CoOx phase at the outermost surface, suppressing the direct contact between CO2 and the metallic Co core.
查看更多>>摘要：? 2022 Elsevier B.V.A highly active and selective GaZrOx/SAPO-34 bifunctional catalyst was developed for CO2 hydrogenation into C2=–C4=. A high C2=–C4= selectivity of 88.8% at CO2 conversion of 26.7% was achieved, and the olefin yield reached 11.3%, outperforming the previous reports. As Ga:Zr atomic ratio increases, the surface oxygen vacancy content (OV), responsible for CO2 activation, firstly increases from 22.5% to 32.6% and then decreases to 15.4%, while the H2 dissociation ability produced by Ga site increases gradually. Activated CO2 at Zr–OV–Zr site could either react with Ga–Hδ– to form HCOO*, then successive hydrogenation to CH3O* intermediate, or combine with O–Hδ+ to form COOH*, followed by dissociation to form CO. The formation of CH3O* or CO is competitive, which highly depends on the H2 dissociation ability, only the moderate H2 dissociation ability benefits CO2 hydrogenation to CH3O* at high temperature, leading to a high C2=–C4= yield.
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