Selective Oxidative Coupling of Methane to Ethylene in a Solid Oxide Electrolyser Based on Porous Single-Crystalline CeO2 Monoliths.

Catalytic conversion of CH4 to C2 H4 plays an important role in the light olefin industry. Here, we report the electrochemical conversion of CH4 to C2 H4 /C2 H6 at the anode with the electrolysis of CO2 to CO at the cathode in a solid oxide electrolyser. We constructed well-defined interfaces that function as three-phase boundaries by exsolving single-crystalline Ni nanoparticles in porous single-crystalline CeO2 monoliths. We engineered the chemical states and flux of active oxygen species for the oxidation of CH4 at the anode by controlling voltage and temperature. We show the unprecedented C2 selectivity (C2 H4 and C2 H6 ) of ≥99.5 % at a CH4 conversion of ≈7 %. The electrolyser exhibits excellent durability without performance degradation being observed in a continuous operation of 100 hours. Our work enables a novel path for the selective conversion of CH4 /CO2 into useful chemicals, and the technique of building well-defined interfaces may find potential applications in other fields.

Electrochemical Oxidative Dehydrogenation of Ethane to Ethylene in a Solid Oxide Electrolyzer.

Oxidative dehydrogenation of ethane to ethylene is an important process in light olefin industry; however, the over-oxidation of ethane leads to low ethylene selectivity. Here, we report a novel approach to electrochemical oxidative dehydrogenation of ethane in anode in conjunction with CO2 reduction at cathode in a solid oxide electrolyser using a porous single-crystalline CeO2 electrode at 600 °C. We identify and engineer the flux and chemical states of active oxygen species that evolve from the lattice at anode surface to activate and dehydrogenate ethane to ethylene via the reaction of epoxy species. Active oxygen species (O2- , O2 2- and O2 - ) at the anode surface effectively dehydrogenate ethane to ethylene, but O- species tend to induce deep oxidation. We demonstrate exceptionally high ethylene selectivity of 95 % and an ethane conversion of 10 % with a durable operation of 300 h.

Titanate cathodes with enhanced electrical properties achieved via growing surface Ni particles toward efficient carbon dioxide electrolysis.

Ionic conduction in perovskite oxide is commonly tailored by element doping in lattices to create charge carriers, while few studies have been focused on ionic conduction enhancement through tailoring microstructures. In this work, remarkable enhancement of ionic conduction in titanate has been achieved via in situ growing active nickel nanoparticles on an oxide surface by controlling the oxide material nonstoichiometry. The combined use of XRD, SEM, XPS and EDS indicates that the exsolution/dissolution of the nickel nanoparticles is completely reversible in redox cycles. With the synergetic effect of enhanced ionic conduction of titanate and the presence of catalytic active Ni nanocatalysts, significant improvement of electrocatalytic performances of the titanate cathode is demonstrated. A current density of 0.3 A cm(-2) with a Faradic efficiency of 90% has been achieved for direct carbon dioxide electrolysis in a 2 mm-thick YSZ-supported solid oxide electrolyzer with the modified titanate cathode at 2 V and 1073 K.

Sr2Fe1.575Mo0.5O6-δ Promotes the Conversion of Methane to Ethylene and Ethane.

Oxidative coupling of methane can produce various valuable products, such as ethane and ethylene, and solid oxide electrolysis cells (SOECs) can electrolyze CH4 to produce C2H4 and C2H6. In this work, Sr2Fe1.575Mo0.5O6-δ electrode materials were prepared by impregnation and in situ precipitation, and Sr2Fe1.5Mo0.5O6-δ was taken as a reference to study the role of metal-oxide interfaces in the catalytic process. When the Fe/Sr2Fe1.575Mo0.5O6-δ interface is well constructed, the selectivity for C2 can reach 78.18% at 850 °C with a potential of 1.2 V, and the conversion rate of CH4 is 11.61%. These results further prove that a well-constructed metal-oxide interface significantly improves the catalytic activity and facilitates the reaction.

Enhancing CO2 electrolysis through synergistic control of non-stoichiometry and doping to tune cathode surface structures.

Sustainable future energy scenarios require significant efficiency improvements in both electricity generation and storage. High-temperature solid oxide cells, and in particular carbon dioxide electrolysers, afford chemical storage of available electricity that can both stabilize and extend the utilization of renewables. Here we present a double doping strategy to facilitate CO2 reduction at perovskite titanate cathode surfaces, promoting adsorption/activation by making use of redox active dopants such as Mn linked to oxygen vacancies and dopants such as Ni that afford metal nanoparticle exsolution. Combined experimental characterization and first-principle calculations reveal that the adsorbed and activated CO2 adopts an intermediate chemical state between a carbon dioxide molecule and a carbonate ion. The dual doping strategy provides optimal performance with no degradation being observed after 100 h of high-temperature operation and 10 redox cycles, suggesting a reliable cathode material for CO2 electrolysis.

Highly Efficient CO2 Electrolysis on Cathodes with Exsolved Alkaline Earth Oxide Nanostructures.

The solid oxide CO2 electrolyzer has the potential to provide storage solutions for intermittent renewable energy sources as well as to reduce greenhouse gas emissions. One of the key challenges remains the poor adsorption and activity toward CO2 reduction on the electrolyzer cathode at typical operating conditions. Here, we show a novel approach in tailoring a perovskite titanate (La, Sr)TiO3+δ cathode surface, by the in situ growing of SrO nanoislands from the host material through the control of perovskite nonstoichiometry. These nanoislands provide very enhanced CO2 adsorption and activation, with stability up to 800 °C, which is shown to be in an intermediate form between carbonate ions and molecular CO2. The activation of adsorbed CO2 molecules results from the interaction of exsolved SrO nanoislands and the defected titanate surface as revealed by DFT calculations. These cathode surface modifications result in an exceptionally high direct CO2 electrolysis performance with current efficiencies near 100%.

Redox-Reversible Iron Orthovanadate Cathode for Solid Oxide Steam Electrolyzer.

A redox-reversible iron orthovanadate cathode is demonstrated for a solid oxide electrolyser with up to 100% current efficiency for steam electrolysis. The iron catalyst is grown on spinel-type electronic conductor FeV2O4 by in situ tailoring the reversible phase change of FeVO4 to Fe+FeV2O4 in a reducing atmosphere. Promising electrode performances have been obtained for a solid oxide steam electrolyser based on this composite cathode.

A green one-pot synthesis of Pt/TiO2/Graphene composites and its electro-photo-synergistic catalytic properties for methanol oxidation.

A facile and green one-pot method was used to synthesize Pt/TiO2/Graphene composites with ethanol as a reducing agent under microwave irradiation. The as-prepared composites were characterized by SEM, TEM, EDX, XPS, XRD and Raman. Electrocatalytic performance of the Pt/TiO2/GNs composites was investigated by cyclic voltammetry (CV), chronoamperometric (CA), COad stripping voltammetry and electrochemical impedance spectrum (EIS). All experimental data have revealed that TiO2 (P25) not only enhanced the reduction ability of ethanol under microwave irradiation but also promoted Pt heterogeneous nucleation to form Pt nanoclusters which are around P25 and loaded on graphene nanosheets (GNs) surface. Electrochemical experiments showed that Pt/TiO2/GNs had much higher catalytic activity and stability toward methanol oxidation reaction (MOR) and better resistance to CO poisoning compared with Pt/GNs and the commercially available Johnson Matthey 20% Pt/C catalyst (Pt/C-JM). Especially under UV irradiation with 20min, Pt/TiO2/GNs composites showed an ultrahigh forward peak current density of 1354mAmg(-1), nearly 2.5 times higher than that of Pt/C-JM, which indicated that the electrocatalytic and photocatalytic properties of Pt/TiO2/GNs had been integrated to boost the catalytic performance for MOR.