gqing Qin

High-performance fuel electrodes based on NbTi0.5M0.5O4 (M = Ni, Cu) with reversible exsolution of the nano-catalyst for steam electrolysis

This paper investigates potential fuel electrode materials NbTi0.5M0.5O4 (M = Ni, Cu) for solid oxide steam electrolysers. Efficient catalytic metallic Ni and Cu nanoparticles are exsolved and anchor onto the surface of the highly electronically conducting material Nb1.33Ti0.67O4, forming an enhanced composite fuel electrode in the in situ reduction. The XRD, SEM, EDS and XPS results together confirm that the exsolution or dissolution of the nanometallic catalyst is completely reversible in the redox cycles. The electrical properties of the reduced NbTi0.5M0.5O4 ceramic fuel electrode is systematically investigated and correlated to the electrochemical performance of the composite fuel electrodes in symmetric cells or electrolysis cells. The synergetic effect of the metallic catalyst and ceramic fuel electrode leads to the excellent stability as well as the superior performance of the direct steam electrolysis without a flow of reducing gas over the composite fuel electrodes. The Faradic efficiencies of the steam electrolysis reach 95% and 97% for the Ni- and Cu-enhanced fuel electrodes on flowing reducing gas over the fuel electrodes, respectively, however, comparable performance is achieved for the direct steam electrolysis with Ni- and Cu-enhanced fuel electrodes without flowing reducing gas over the composite fuel electrodes.

In situ formation of oxygen vacancy in perovskite Sr 0.95 Ti 0.8 Nb 0.1 M 0.1 O 3 (M = Mn, Cr) toward efficient carbon dioxide electrolysis

In this work, redox-active Mn or Cr is introduced to the B site of redox stable perovskite Sr0.95Ti0.9Nb0.1O3.00 to create oxygen vacancies in situ after reduction for high-temperature CO2 electrolysis. Combined analysis using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric analysis confirms the change of the chemical formula from oxidized Sr0.95Ti0.9Nb0.1O3.00 to reduced Sr0.95Ti0.9Nb0.1O2.90 for the bare sample. By contrast, a significant concentration of oxygen vacancy is additionally formed in situ for Mn- or Cr-doped samples by reducing the oxidized Sr0.95Ti0.8Nb0.1M0.1O3.00 (M = Mn, Cr) to Sr0.95Ti0.8Nb0.1M0.1O2.85. The ionic conductivities of the Mn- and Cr-doped titanate improve by approximately 2 times higher than bare titanate in an oxidizing atmosphere and 3–6 times higher in a reducing atmosphere at intermediate temperatures. A remarkable chemical accommodation of CO2 molecules is achieved on the surface of the reduced and doped titanate, and the chemical desorption temperature reaches a common carbonate decomposition temperature. The electrical properties of the cathode materials are investigated and correlated with the electrochemical performance of the composite electrodes. Direct CO2 electrolysis at composite cathodes is investigated in solid-oxide electrolyzers. The electrode polarizations and current efficiencies are observed to be significantly improved with the Mn- or Cr-doped titanate cathodes.

All solid supercapacitors based on an anion conducting polymer electrolyte

In this paper, KOH doped polybenzimidazole (PBI–KOH), an anion conducting polymer electrolyte, has been employed to demonstrate the possibility of fabricating alkaline all solid supercapacitors. This is different from the conventional gel-electrolyte based quasi-solid supercapacitors. Symmetric devices assembled using commercial activated carbon based electrodes and PBI–KOH electrolytes exhibit a high rate capability with specific capacitance retention above 90% when the discharge current density increased from 0.5 to 20 A g−1. However, PBI–KOH suffers from low cycling stability with a rapid decrease in specific capacitance in the first 1000 cycles. By adding a binder or narrowing the potential window, the cycling stability could be improved. The best device shows a quite stable performance during the first 2000 cycles with specific capacitance degradation of less than 5%. An asymmetric (or hybrid) device has been assembled using activated carbon and Ni(OH)2 as electrode materials, which exhibits a relative high specific energy of 37.1 W h kg−1. These results strongly recommend the great potential of solid anion conducting polymer electrolytes in developing alkaline all solid supercapacitors.

Composite titanate cathode decorated with heterogeneous electrocatalytic sites towards efficient carbon dioxide electrolysis

The coupling of surface oxygen vacancies with nano-sized metal can effectively improve the catalytic activity of heterogeneous catalysts. In this work, a high concentration of oxygen vacancies is created in Mn-doped titanate cathode, then iron nanoparticles are exsolved to anchor on the titanate surface and combine the surface oxygen vacancies to form heterogeneous catalysis clusters. The active Mn in the B site of the redox-stable Sr0.95Ti0.8Nb0.1Mn0.1O3.00 (STNMO) creates 0.15 mol oxygen vacancies in the reduced Sr0.95Ti0.8Nb0.1Mn0.1O2.85. With iron doping in the B site, it is found that the exsolution and dissolution of the iron nanoparticles are completely reversible on the titanate surface in redox cycles. The presence of iron nano crystal remarkably increases the ionic conductivity of the titanate solid solution by 0.5 orders of magnitude at intermediate temperatures. Promising electrode polarizations are obtained based on the titanate cathode decorated with heterogeneous electrocatalytic clusters in symmetric cells. The current efficiencies of direct carbon dioxide electrolysis reach as high as 90% in an oxide-ion conducting solid oxide electrolyzer at high temperatures.

Efficient carbon dioxide electrolysis based on ceria cathode loaded with metal catalysts

Fluorite-type heterogeneous catalyst ceria is a mixed conductor and widely used as a hydrocarbon-fueled solid oxide fuel cell anode because of its advantage of anti-carbon deposition, redox stability, and thermal compatibility. However, the electrocatalytic activity of a ceria cathode is limited for the catalysis of electrochemical oxidation or reduction reactions. In this work, catalytic-active iron and nickel catalysts are loaded onto a ceria cathode via an infiltration method to enhance electrode performance. Direct electrolysis of carbon dioxide is performed on ceria cathodes loaded with iron and nickel catalysts in solid oxide electrolyzers, respectively. The polarization resistance of symmetrical cells and electrolysis cells loaded with nickel and iron catalysts is largely improved in comparison with the bare ceria. The current efficiencies for carbon dioxide electrolysis for the iron- and nickel-loaded cathodes are 76 and 80 % at 2.0 V and 800 °C, respectively, approximately 25 % higher than that for the bare ceria cathode.

Demonstration of efficient electrochemical biogas reforming in a solid oxide electrolyser with titanate cathode

Biogas reforming is a renewable and promising way to produce syngas. In this work, we demonstrate a novel strategy to directly and electrochemically convert CH4–CO2 into H2–CO. Electrochemical reforming of dry CH4–CO2 (1 : 1) mixture is successfully achieved in a 10 μm-thick titanate cathode with oxygen byproduct generated in anode in an oxide-ion-conducting solid oxide electrolyser under external voltages. In addition, loading iron nanocatalyst in titanate cathode or/and increasing applied voltages has further improved CH4–CO2 conversion. The highest methane conversion of approximately 80% is demonstrated for direct electrochemical reforming in cathode in contrast to the low conversion under open circuit condition in oxide-ion-conducting solid oxide electrolyser cathode.

Enhanced High-Temperature Cyclic Stability of Al-Doped Manganese Dioxide and Morphology Evolution Study Through in situ NMR under High Magnetic Field

In this work, Al-doped MnO2 (Al-MO) nanoparticles have been synthesized by a simple chemical method with the aim to enhance cycling stability. At room temperature and 50 °C, the specific capacitances of Al-MO are well-maintained after 10 000 cycles. Compared with pure MnO2 nanospheres (180.6 F g-1 at 1 A g-1), Al-MO also delivers an enhanced specific capacitance of 264.6 F g-1 at 1 A g-1. During the cycling test, Al-MO exhibited relatively stable structure initially and transformed to needlelike structures finally both at room temperature and high temperature. In order to reveal the morphology evolution process, in situ NMR under high magnetic field has been carried out to probe the dynamics of structural properties. The 23Na spectra and the SEM observation suggest that the morphology evolution may follow pulverization/reassembling process. The Na+ intercalation/deintercalation induced pulverization, leading to the formation of tiny MnO2 nanoparticles. After that, the pulverized tiny nanoparticles reassembled into new structures. In Al-MO electrodes, doping of Al3+ could slow down this structure evolution process, resulting in a better electrochemical stability. This work deepens the understanding on the structural changes in faradic reaction of pseudocapacitive materials. It is also important for the practical applications of MnO2-based supercapacitors.