Jian-Hui Li

A-site deficient perovskite: the parent for in situ exsolution of highly active, regenerable nano-particles as SOFC anodes

Chemical deposition is widely used to enhance the performance of perovskite anodes for solid oxide fuel cells (SOFCs). However, the anodes thus produced still have unsatisfactory activity and experience reproducibility problems. For the first time, this paper reports that the in situ exsolution of nano-Ni could be facilitated on Ni-doped (La0.7Sr0.3)CrO3 (LSCNi) anodes with A-site deficiency, showing a maximum power density of 460 mW cm−2 in 5000 ppm H2S–H2 compared to only 135 mW cm−2 of fuel cells with stoichiometric LSCNi. Besides, the fuel cell also demonstrates desirable redox stability in sour fuel. The introduction of A-site deficiency can help the formation of highly mobile oxygen vacancies and remarkably enhance the reducibility of Ni nano-particles, thus significantly increasing electronic conductivity and catalytic activity simultaneously. Such fabricated perovskite has the potential to be decorated with diverse nano-active particles for a wide range of applications in industrial fields.

New Opportunity for in Situ Exsolution of Metallic Nanoparticles on Perovskite Parent

One of the main challenges for advanced metallic nanoparticles (NPs) supported functional perovskite catalysts is the simultaneous achievement of a high population of NPs with uniform distribution as well as long-lasting high performance. These are also the essential requirements for optimal electrode catalysts used in solid oxide fuel cells and electrolysis cells (SOFCs and SOECs). Herein, we report a facile operando manufacture way that the crystal reconstruction of double perovskite under reducing atmosphere can spontaneously lead to the formation of ordered layered oxygen deficiency and yield segregation of massively and finely dispersed NPs. The real-time observation of this emergent process was performed via an environmental transmission electron microscope. Density functional theory calculations prove that the crystal reconstruction induces the loss of coordinated oxygen surrounding B-site cations, serving as the driving force for steering fast NP growth. The prepared material shows promising capability as an active and stable electrode for SOFCs in various fuels and SOECs for CO2 reduction. The conception exemplified here could conceivably be extended to fabricate a series of supported NPs perovskite catalysts with diverse functionalities.

Highly Active and Redox-Stable Ce-Doped LaSrCrFeO-Based Cathode Catalyst for CO2 SOECs

Lanthanum chromate-based perovskite oxides have attracted great attention as the cathode materials in the high-temperature CO2 electrolysis because of its good redox stability. However, the unsatisfied electrochemical catalytic activity and insufficient adsorption of CO2 at operating temperature still hindered the further improvement of electrochemical performance and the Faraday efficiency of the electrolysis cell. In this work, the catalytic and redox active Ce was doped into A site of La0.7Sr0.3Cr0.5Fe0.5O3-δ (LSCrF) to promote the catalytic performance, and to introduce oxygen vacancies in the lattice in situ after reduction under the operational condition. The increased amount of oxygen vacancies not only facilitates the mobility of oxygen ions, but also provides favorable accommodation for chemical adsorption of CO2. The CO2 electrolysis tests demonstrated the superior electrochemical performances, higher Faraday efficiencies of the Ce-doped LSCrF cathode catalyst in comparison with that without Ce doping, indicating the perspective application of this functional material.

Cobalt doped LaSrTiO3−δ as an anode catalyst: effect of Co nanoparticle precipitation on SOFCs operating on H2S-containing hydrogen

This article compares the effects of Co doping on phase structures and stability of lanthanum strontium titanate (LST) anodes and electrochemical measurements in solid oxide fuel cells (SOFCs) employing H2S-containing H2 as fuel. The Co-doped LST (LSCT) with a perovskite structure was synthesized via a solid state approach, achieving excellent phase purity and refined particle size. The catalytic activity and electrochemical performance are significantly improved by introducing Co. A maximum power density of 300 mW cm−2 was achieved at 900 °C with 5000 ppm H2S–H2 in a fuel cell having a 300 μm thick YSZ electrolyte. Trace amounts of metallic Co nanoparticles with sizes typically no larger than 10 nm in diameter were detected on the LSCT surface after reduction in H2 at 900 °C. The nano-sized Co clusters could reduce the anode polarization resistance, as well as improve the cell performance, compared with undoped LST anodes. The LSCT anode catalyst was electrochemically stable in 5000 ppm H2S–H2 during the test time at high operating temperature. The LSCT anode catalyst also had relatively high redox stability in reversible oxidation–reduction cycles.

Electrodeposition of manganese dioxide film on activated carbon paper and its application in supercapacitors with high rate capability

In this research magnesium dioxide (MnO2) is electrodeposited over activated carbon paper (ACP) to form a composited MnO2/ACP material. The as-prepared MnO2/ACP shows excellent capacitance performance with a high specific capacitance of 485.4 F g−1 calculated from a discharge curve with current density 2.0 A g−1, owing to its enlarged specific surface area and improved electronic conductivity. Moreover, the MnO2/ACP possesses remarkable rate capability due to the easy access of electrolytic ions, leading to complete utilization of MnO2 active material for supercapacitors. To summarize, the electrodeposition of MnO2 thin film on activated carbon paper is reported for the first time, and the composited MnO2/ACP is a promising electrode material for building up efficient supercapacitors.

A-site deficient chromite perovskite with in situ exsolution of nano-Fe: a promising bi-functional catalyst bridging the growth of CNTs and SOFCs

For the first time, an iron doped lanthanum strontium chromite with A-site deficiency (A-LSCFe) was fabricated and utilized as an effective bi-functional catalyst for the growth of multi-wall carbon nanotubes (MWCNTs) and solid oxide fuel cells (SOFCs). The introduction of A-site deficiency significantly facilitates the in situ exsolution of nano-iron particles on which considerable amounts of MWCNTs are grown. The material was also used as the anode catalyst for SOFCs and proved to be a very effective anode catalyst in comparison with the stoichiometric material (sto-LSCFe). The exsolved nano-iron particles on A-LSCFe provide many more active sites for the oxidation reaction of fuel, leading to sharp enhancement of the electrochemical performance of the cell. It is also discovered that the growth of MWCNTs with high electron conductivity leads to a further improvement of the electricity output.

Correction: An ingenious Ni/Ce co-doped titanate based perovskite as a coking-tolerant anode material for direct hydrocarbon solid oxide fuel cells

Correction for ‘An ingenious Ni/Ce co-doped titanate based perovskite as a coking-tolerant anode material for direct hydrocarbon solid oxide fuel cells’ by Yi-Fei Sun et al., J. Mater. Chem. A, 2015, 3, 22830–22838.

Enhancing Perovskite Electrocatalysis of Solid Oxide Cells Through Controlled Exsolution of Nanoparticles

Perovskite oxides have received a great deal of attention as promising electrodes in both solid oxide fuel cells (SOFCs) and solid oxide electrolyzer cells (SOECs) because of their reasonable reactivity, impurity tolerance, and tunable properties. In particular, exploration is still required for improving perovskite electrodes, which normally suffer from slow kinetics in electrocatalysis. Experimental studies have led to the development of new classes of perovskites with advanced characteristics and electrode kinetics at technical levels. In parallel with those developments, achievements in theoretical and computational studies have led to substantial understanding, at the atomic level, of their physicochemical properties and electrocatalytic behaviors. Their chemical and structural flexibilities enable perovskites to accommodate most metallic elements without destroying their complex matrix structures, thereby delivering a pathway to engineer their catalytic properties. In this Minireview, recent advances in perovskite electrodes are introduced, and perovskites with exsolved nanoparticles are discussed as enhanced electrocatalytic materials.

Boosting visible light photo-/Fenton-catalytic synergetic activity of BiOIO3 by coupling with Fe2O3

The combination of a semiconductor photocatalyst with guest transition metal oxides can extend its light absorption property in the visible region, leading to the emergence of potential catalysts for solar photocatalytic degradation. In the present study, Fe2O3/BiOIO3 nanosheets with heterojunction couples have been fabricated in one-step by a simple hydrothermal method and used as a heterogeneous Fenton-like photocatalyst for the oxidative degradation of p-nitrophenol (PNP) under visible light. The absorption range of BiOIO3 extended to the visible light region with the introduction of Fe, while the band gap is dramatically decreased from 3.00 eV for pure BiOIO3 to 1.81 eV for 30% Fe2O3/BiOIO3. The recombination of photogenerated electron–hole pairs can also be prevented effectively. The intrinsic relationship between structure and catalytic activity was fully studied and a possible catalytic mechanism was proposed. The enhanced photocatalytic activity can be attributed to the synergistic effect of heterojunction semiconductor photocatalysis and heterogeneous Fenton catalysis caused by BiOIO3 and Fe2O3. This highly active heterogeneous catalyst has the potential for efficient utilization of solar energy in the visible range and can be applied in environmental remediation and waste water treatment.

Determination of phthalate esters in airborne particulates by heterogeneous photo-Fenton catalyzed aromatic hydroxylation fluorimetry

The environmental contaminants phthalic acid esters (PAEs) were determined by aromatic hydroxylation fluorimetry combined with heterogeneous photo-Fenton process in the presence of vermiculite supported BiFeO3 (VMT-BiFeO3). In strong alkaline solution, PAEs were hydrolyzed into phthalates with no fluorescence, which then reacted with hydroxyl free radicals produced in photo-Fenton process catalyzed by VMT-BiFeO3 to form the fluorescent hydroxyl phthalates. The fluorescence intensity was proportional to the concentration of PAEs with the maximum excitation and emission wavelength of 300nm and 417nm, respectively. A good linear relationship can be obtained in the range of 3.8×10-7 to 4.8×10-5molL-1 for DEP with correlation coefficient of 0.9997, and the sensitivity of the method was high with detection limit of 5.43×10-8molL-1. The method has been successfully applied to determine total PAEs in airborne particulates with satisfactory results.