Jing-Li Luo

Progress in La-doped SrTiO3 (LST)-based anode materials for solid oxide fuel cells

Solid oxide fuel cells (SOFCs) have appeared as a promising technology for a wide variety of potential commercial applications to lessen the urgency of energy shortage and environmental pollution associated with using conventional fossil fuels. Among the worldwide SOFCs research activities, the progress of SOFCs fed with hydrocarbon fuels that contain trace amount of H2S is one of the most important research directions. Thereby, it becomes crucial to design novel electrode materials with enhanced catalytic activity, stability and tolerances to carbon deposition and sulfur poisoning. La-substituted SrTiO3 (LST) based perovskite anodes have been widely investigated because of their high electronic conductivity in reducing atmospheres, excellent dimensional and chemical stability upon redox cycling and outstanding sulfur and coking tolerances. In this review paper, we will describe the development of LST-based anode materials for SOFCs in recent years. The synthesis, structure and fuel cell performance of the doped LST and LST-based composite anode materials are summarized in detail. The mechanism of H2S-induced enhancement effect for electrochemical reactions on the LST-based anode materials is explored. The challenges related to the future developments of LST-based anode materials for SOFCs are also discussed.

Electrochemical characterization of copper surface modified by n-alkanethiols in chloride-containing solutions

The self-assembled monolayers (SAMs) of three n-alkanethiols, 1-octadecanethiol (C18SH), 1-dodecanethiol (C12SH), and 1-hexanethiol (C6SH), were formed on the fresh copper surface pretreated by nitric acid etch. The surface properties of the alkanethiol modified copper electrode in chloride-containing solutions were electrochemically characterized. The polarization measurements have shown that alkanethiol SAMs onto copper were able to protect effectively the underlying copper against corrosion. The cyclic voltammetric results, together with FT-IR measurements, showed that alkanethiol SAMs had quite good anodic inhibition at the lower anodic potentials, but this inhibition action gradually lost because of removal of SAMs from the copper substrate with the increase of anodic potentials. Alkanethiol SAMs were proved to be defective by scanning Kelvin probe (SKP) measurements. Electrochemical noise (EN) experiments have shown that SAMs-covered copper electrode suffered pitting attack in HCl solutions. The formation mechanism of pits was explained in this paper

Shape-Dependent Electrocatalytic Reduction of CO2 to CO on Triangular Silver Nanoplates

Electrochemical reduction of CO2 (CO2RR) provides great potential for intermittent renewable energy storage. This study demonstrates a predominant shape-dependent electrocatalytic reduction of CO2 to CO on triangular silver nanoplates (Tri-Ag-NPs) in 0.1 M KHCO3. Compared with similarly sized Ag nanoparticles (SS-Ag-NPs) and bulk Ag, Tri-Ag-NPs exhibited an enhanced current density and significantly improved Faradaic efficiency (96.8%) and energy efficiency (61.7%), together with a considerable durability (7 days). Additionally, CO starts to be observed at an ultralow overpotential of 96 mV, further confirming the superiority of Tri-Ag-NPs as a catalyst for CO2RR toward CO formation. Density functional theory calculations reveal that the significantly enhanced electrocatalytic activity and selectivity at lowered overpotential originate from the shape-controlled structure. This not only provides the optimum edge-to-corner ratio but also dominates at the facet of Ag(100) where it requires lower energy to initiate the rate-determining step. This study demonstrates a promising approach to tune electrocatalytic activity and selectivity of metal catalysts for CO2RR by creating optimal facet and edge site through shape-control synthesis.

Use of Metal Sulfides as Anode Catalysts in H 2 S -Air SOFCs

Anode catalysts comprising MoS 2 and composite metal sulfides have been investigated for electrochemical oxidation of hydrogen sulfide in solid oxide fuel cells (SOFCs) at temperatures up to 850°C. All catalysts exhibited good electrical conductivity and catalytic activity at all temperatures. MoS 2 and composite catalysts were found to be more active than Pt, an established catalyst for high-temperature H 2 S-air fuel cells at 650-830°C. However, MoS 2 itself sublimes above 450°C. In contrast, composite catalysts (M-Mo-S) derived from a mixture of sulfides of Mo and other transition metals (Fe, Co, Ni) have been shown to be stable and effective for electrochemical conversion of H 2 S in SOFCs up to 850°C. Electrical contact is poor between platinum current collecting layers and metal sulfide anode catalysts. This problem has been overcome by mechanically mixing conductive Ag powder into the anode layer, instead of applying a thin layer of platinum to the anode.

Effects of oxide additions on electrochemical hydriding and dehydriding behavior of Mg2Ni-type hydrogen storage alloy electrode in 6 M KOH solution

Effects of metal oxide additions on the electrochemical hydriding and dehydriding behavior of Mg2Ni-type hydrogen storage alloy in 6 M KOH aqueous solution were investigated. The electrode characteristics of mechanically alloyed composites of Mg1.9Y0.1Ni0.9Al0.1–5 wt% MO (MO=Ag2O, Fe2O3, MoO3, RuO2 and V2O5) were examined such as discharge capacity, high-rate dischargability and cycle life. The discharge capacity and high-rate dischargability were greatly increased by the modification with the oxide additions, but the cycle life decreased. The electrochemical performances were characterized using both dc polarization and ac impedance analysis techniques. The hydrogen diffusivity in the alloys was estimated by an electrochemical method.

Analysis of the role of electrode capacitance on the initiation of pits for A516 carbon steel by electrochemical noise measurements

The fluctuations of potential and current of A516 carbon steel were monitored in chloride solution. Different noise patterns were observed during the incubation and initiation periods of pitting. During the incubation of pits, the fluctuations of potential were in phase with the current fluctuations, indicating that the faradaic current plays a major role in pit incubation. The initiation of pitting was characterized by sharp fluctuations of potential and current. The slower recovery of potential always exceeded the time for the recovery of the current. This was attributed to the slow discharging of the capacitance on the electrode surface. The capacitance plays a major role on potential fluctuations generated during pitting of carbon steel.

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.

Electronic band structure of passive film on X70 pipeline steel

Abstract Mott-Schottky analyses and photoelectrochemical measurements were used to explore the effects of film formation potentials, time, and chloride ions on the electronic properties of the passive film on X70 pipeline steel in 0.5 M NaHCO 3 . Mott-Schottky analyses showed that with increasing film formation potentials, the capacitance and donor density of the passive film decrease, and the flat band potential and thickness of the space charge layer increases. The addition of chloride ions increases the capacitance and donor density of the film and results in a more negative flat band potential and a thinner space charge layer. Photoelectrochemical measurements imply that photo-generated carriers with a low mobility exist in the passive film and the photocurrents of the film increase when the film formation potential becomes more positive. The bandgap energy, E g , of the passive film decreases with increasing film formation potentials. The extension of film formation time increases the photocurrents and leads to a decrease in the bandgap energy of the passive film. The effect of film formation time on the photocurrents of the film formed at 0.6 V SCE was less remarkable than that formed at 0.2 V SCE . The existence of chloride ions in 0.5 M NaHCO 3 decreases the photocurrents and increases the bandgap energy of the passive film.

Novel layered solid oxide fuel cells with multiple-twinned Ni0.8Co0.2 nanoparticles: the key to thermally independent CO2 utilization and power-chemical cogeneration

To energy-efficiently offset our carbon footprint, we herein developed a novel CH4–CO2 dry reforming process to co-produce electricity and CO-concentrated syngas, which takes advantage of the selective oxidation of H2 in high performance proton-conducting solid oxide fuel cells (SOFCs). In these cells, an additional functional layer, consisting of a Ni0.8Co0.2–La0.2Ce0.8O1.9 (NiCo–LDC) composite, was successfully incorporated into the anode support, forming a layered SOFC configuration. The multiple-twinned bimetallic nanoparticles were then proven to have superior activity towards in situ dry reforming. In comparison to the conventional design, this layered SOFC demonstrated drastically improved CO2 resistance as well as internal reforming efficiency (CO2 conversion reached 91.5% at 700 °C), and up to 100 h galvanostatic stability in a CH4–CO2 feedstream at 1 A cm−2. More importantly, H2 was effectively and exclusively converted by electrochemical oxidation, yielding no CO2 but CO concentrated syngas in the anode effluent. The maximum power density exceeded 910 mW cm−2 at 700 °C with a polarization resistance as low as 0.121 Ω cm2. Consequently, the heat released by H2 electrochemical oxidation fully compensated for that required by the extremely endothermic dry reforming reaction, making the entire process thermally self-sufficient. We also showed that the layered design was beneficial in terms of decreasing coking and increasing CO2 resistance of the SOFC in the mixed CO2 and CH4 feedstock. This novel process promises to play a pivotal role in future CO2 conversion and utilization.

High-Performance Anode for H 2 S ­ Air SOFCs

A high-performance composite anode has been developed for H 2 S-air solid oxide fuel cells (SOFCs). The anode design is based on the requirements of three-phase boundary theory. The anode material comprises a mixture of composite metal sulfide (Mo-Ni-S) catalyst prepared from MoS 2 and NiS (1:1 weight ratio), admixed with up to 10% each of Ag as electronic conductor and yttria-stabilized zirconia (YSZ) as ionic conductor. The optimum composition is about 90 wt % Mo-Ni-S, 5 wt % Ag, and 5 wt % YSZ. A fuel cell using a 0.2 mm thick YSZ membrane produced a maximum sustainable current density over 480 mA cm -2 at at 750°C and over 800 mA cm -2 at 850°C, and maximum power density 50 mW cm -2 at 750°C and over 200 mW cm -2 at 850°C.