• Energy Research

Developing a low-cost, and highly-efficient catalysts for improving oxygen reduction reaction (ORR) is imperative to the energy storage and conversion device. Here, we synthesized Ag/La0.6Sr0.4CoO3-delta, (Ag/LSC) composites by decorating LSC with Ag using the electroless technique. As a result, the LSC was homogenously overlaid with Ag nanoparticles. The derived Ag/LSC composites possessed a relatively higher specific surface area than pure LSC and Ag. The Co-O-Ag bonds in the composites contribute substantial electrons transferred from Ag to Co element, resulting in the unique electronic structures and strong electronic interaction between Ag and LSC. The significant improvements of ORR activity in alkaline solution at room temperature can be observed in Ag/LSC composites compared to the pure Ag and LSC. The composites with optimal Ag loading (50 wt%) showed best ORR activity among all the composites according to the half-wave potential and diffusion limiting current density. The presented strategy of silver surface modification via electroless process can provide effective routes for designing high performance metal oxide (e.g. perovskite) composite electrocatalysts. (C) 2018 The Electrochemical Society.

AbstractSimultaneously enhancing the reaction kinetics, mass transport, and gas release during alkaline hydrogen evolution reaction (HER) is critical to minimizing the reaction polarization resistance, but remains a big challenge. Through rational design of a hierarchical multiheterogeneous three‐dimensionally (3D) ordered macroporous Mo2C‐embedded nitrogen‐doped carbon with ultrafine Ru nanoclusters anchored on its surface (OMS Mo2C/NC‐Ru), we realize both electronic and morphologic engineering of the catalyst to maximize the electrocatalysis performance. The formed Ru‐NC heterostructure shows regulative electronic states and optimized adsorption energy with the intermediate H*, and the Mo2C‐NC heterostructure accelerates the Volmer reaction due to the strong water dissociation ability as confirmed by theoretical calculations. Consequently, superior HER activity in alkaline solution with an extremely low overpotential of 15.5 mV at 10 mA cm−2 with the mass activity more than 17 times higher than that of the benchmark Pt/C, an ultrasmall Tafel slope of 22.7 mV dec−1, and excellent electrocatalytic durability were achieved, attributing to the enhanced mass transport and favorable gas release process endowed from the unique OMS Mo2C/NC‐Ru structure. By oxidizing OMS Mo2C/NC‐Ru into OMS MoO3‐RuO2 catalyst, it can also be applied as efficient oxygen evolution electrocatalyst, enabling the construction of a quasi‐symmetric electrolyzer for overall water splitting. Such a device's performance surpassed the state‐of‐the‐art Pt/C || RuO2 electrolyzer. This study provides instructive guidance for designing 3D‐ordered macroporous multicomponent catalysts for efficient catalytic applications.

Abstract Proton conducting solid oxide fuel cells are solid state electrochemical devices for power generation at a conversion efficiency (>60%) higher than conventional thermal power plants (∼40%). The cathode is the key component of proton conducting solid oxide fuel cells as it contributes to more than 50% of the total overpotential loss of an H+-SOFC with thin film electrolyte. This work aims to develop high performance and durable cathode for proton conducting solid oxide fuel cells by doping Ba2+ into the Sr-site of the SrSc0.175Nb0.025Co0.8O3-δ perovskite oxide. The influence of moisture on the catalytic activity of Ba0.5Sr0.5Sc0.175Nb0.025Co0.8O3-δ cathode was investigated using electrochemical impedance spectroscopy of symmetric cell at 600 °C. The resistance in the low-frequency range was found to be the rate-limiting step of the oxygen reduction reaction in the dry air, while the resistance in the medium-frequency range became the rate-limiting step in the moist air. With a Ba0.5Sr0.5Sc0.175Nb0.025Co0.8O3-δ cathode, a proton conducting single cell achieved good performance at a temperature of 700 °C with a power density of 633 mW cm−2. However, the performance of single cell decreased with time, probably due to the agglomeration of cathode particles and the coverage of produced water on the active surface. To improve the durability of the proton conducting solid oxide fuel cell, it is critical to minimize the cathode particle agglomeration and remove the produced water effectively. The research results contribute to the development of high-performance fuel cell for efficient energy conversion.

Abstract The use of industrial coal char as a fuel source for an anode-supported solid oxide-based carbon fuel cell (SO-CFC) with a yttrium-stabilized zirconia electrolyte and La0.8Sr0.2MnO3 cathode was investigated. Both the Boudouard reactivity and electrochemical performance of the coal char samples are higher than those of activated carbon samples under the same conditions. The inherent catalytic activity of the metal species (FemOn, CaO, etc.) in the coal char mineral matter leads to good cell performance, even in the absence of an external catalyst. For example, the peak power density of a cell fueled with pure coal char is 100 mW cm−2 at 850 °C, and that of a cell fueled with coal char impregnated with an FemOn-alkaline metal oxide catalyst is 204 mW cm−2. These results suggest that using coal char as the fuel in SO-CFCs might be an attractive way to utilize abundant coal resources cleanly and efficiently, providing an alternative for future power generation.

Improved performance of proton ceramic electrochemical cells (PCECs) through material development and structural design, and application of PCECs for efficient energy conversion render them promising for clean energy and sustainable development.

The outstanding OER performance of a perovskite can be achieved by the strategy of introducing multi-element synergy and building an ordered structure.

We report a hybrid battery that integrates a Zn-Ag battery and a Zn-air battery to utilize the unique advantages of both battery systems. In the positive electrode, Ag nanoparticles couple the discharge behaviors through the two distinct electrochemical systems by working as the active reactant and the effective catalyst in the Zn-Ag and Zn-air reactions, respectively. In the negative electrode, in situ grown Zn particles provide large surface areas and suppress the dendrite, enabling the long-term operating safety. The battery first exhibits two-step voltage plateaus of 1.85 and 1.53 V in the Zn-Ag reaction, after which a voltage plateau of 1.25 V is delivered in the Zn-air reaction, and the specific capacity reaches 800 mAh gZn-1. In addition, excellent reversibility and stability with maintaining high energy efficiency of 68% and a capacity retention of nearly 100% at 10 mA cm-2 are demonstrated through 100 cycles, outperforming both conventional Zn-air and Zn-Ag batteries. This work brings forth a conceptually novel high-performance battery, and more generally opens up new vistas for developing hybrid electrochemical systems by integrating the advantages from two distinct ones.