Co-electrolysis of H2O and CO2 on exsolved Ni nanoparticles for efficient syngas generation at controllable H2/CO ratios

Syngas (CO+H2) is a key-intermediate for the production of liquid fuels via the Fischer-Tropsch process. An emerging technology for generating syngas is the co-electrolysis of H2O/CO2 in solid oxide cells powered by renewable electricity. An application of this technology, however, is still challenging because the Ni-based cermet fuel electrodes are susceptible to degradation under redox and coking conditions, requiring protective hydrogen atmosphere to maintain stable operation. Perovskite oxides are the most promising alternatives due to their redox stability, extensive range of functionalities and the exsolution concept. The latter allows perovskites to be decorated with uniformly dispersed Ni nanoparticles with unique functionalities that can dramatically enhance the performance. Herein, we demonstrate the advantage of employing a nanoparticle-decorated La0.43Ca0.37Ni0.06Ti0.94O3 (LCT-Ni) perovskite to efficiently generate syngas at adjustable H2/CO ratios and simultaneously avoid the need of a reducing agent, hence decreasing the total cost and complexity of the process

Rational Design of Photoelectrodes for the Fully Integrated Polymer Electrode Membrane–Photoelectrochemical Water-Splitting System: A Case Study of Bismuth Vanadate

Photoelectrochemical (PEC) reactors based on polymer electrolyte membrane (PEM) electrolyzers are an attractive alternative to improve scalability compared to conventional monolithic devices. To introduce narrow band gap photoabsorbers such as BiVO4 in PEM-PEC system requires cost-effective and scalable deposition techniques beyond those previously demonstrated on monolithic FTO-coated glass substrates, followed by the preparation of membrane electrode assemblies. Herein, we address the significant challenges in coating narrow band gap metal-oxides on porous substrates as suitable photoelectrodes for the PEM-PEC configuration. In particular, we demonstrate the deposition and integration of W-doped BiVO4 on porous conductive substrates by a simple, cost-effective, and scalable deposition based on the SILAR (successive ionic layer adsorption and reaction) technique. The resultant W-doped BiVO4 photoanode exhibits a photocurrent density of 2.1 mA·cm–2, @1.23V vs RHE, the highest reported so far for the BiVO4 on any porous substrates. Furthermore, we integrated the BiVO4 on the PEM-PEC reactor to demonstrate the solar hydrogen production from ambient air with humidity as the only water source, retaining 1.55 mA·cm–2, @1.23V vs RHE. The concept provides insights into the features necessary for the successful development of materials suitable for the PEM-PEC tandem configuration reactors and the gas-phase operation of the reactor, which is a promising approach for low-cost, large-scale solar hydrogen production.</p

Plasma Driven Exsolution for Nanoscale Functionalization of Perovskite Oxides

Perovskite oxides with dispersed nanoparticles on their surface are considered instrumental in energy conversion and catalytic processes. Redox exsolution is an alternative method to the conventional deposition techniques for directly growing well-dispersed and anchored nanoarchitectures from the oxide support through thermochemical or electrochemical reduction. Herein, a new method for such nanoparticle nucleation through the exposure of the host perovskite to plasma is shown. The applicability of this new method is demonstrated by performing catalytic tests for CO2 hydrogenation over Ni exsolved nanoparticles prepared by either plasma or conventional H2 reduction. Compared to the conventional thermochemical H2 reduction, there are plasma conditions that lead to the exsolution of a more than ten times higher Ni amount from a lanthanum titanate perovskite, which is similar to the reported values of the electrochemical method. Unlike the electrochemical method, however, plasma does not require the integration of the material in an electrochemical cell, and is thus applicable to a wide range of microstructures and physical forms. Additionally, when N2 plasma is employed, the nitrogen species are stripping out oxygen from the perovskite lattice, generating a key chemical intermediate, such as NO, rendering this technology even more appealing.</p

Polymeric Electrolyte Membrane Photoelectrochemical (PEM-PEC) Cell with a Web of Titania Nanotube Arrays as Photoanode and Gaseous Reactants

A novel photoelectrochemical (PEC) cell design is proposed and investigated for H2 production with gaseous reactants. The core of the cell is a membrane electrode assembly (MEA) that consists of a TiO2 photoanode of nanotube arrays, a Pt/C counter and reference electrodes and a polymeric electrolyte membrane (PEM) with proton conductivity, which serves both as compact reactor for water splitting and as gas separator. The design was inspired by PEM electrolysis technology and modified appropriately for allowing illumination and it is also equipped with a third compartment which enables the use of a hydrogen reference electrode. Photoanodes of titania nanotube arrays, TNTAs, were developed, for the first time, on a Ti-web of microfiber substrates, by electrochemical anodization. The performance of TNTAs/Ti-web photoanodes were evaluated in both gaseous and liquid reactants. Due to the presence of reliable reference electrode in gas phase direct comparison of the results was possible. Gas phase operation with He or Air as carrier gases and only 2.5% of water content exhibits very promising photoefficiency in comparison with conventional PEC cells

Hydrogen from electrochemical reforming of C1–C3 alcohols using proton conducting membranes

This study investigates the production of hydrogen from the electrochemical reforming of short-chain alcohols (methanol, ethanol, iso-propanol) and their mixtures. High surface gas diffusion Pt/C electrodes were interfaced to a Nafion polymeric membrane. The assembly separated the two chambers of an electrochemical reactor, which were filled with anolyte (alcohol�+�H2O or alcohol�+�H2SO4) and catholyte (H2SO4) aqueous solutions. The half-reactions, which take place upon polarization, are the alcohol electrooxidation and the hydrogen evolution reaction at the anode and cathode, respectively. A standard Ag/AgCl reference electrode was introduced for monitoring the individual anodic and cathodic overpotentials. Our results show that roughly 75% of the total potential losses are due to sluggish kinetics of the alcohol electrooxidation reaction. Anodic overpotential becomes larger as the number of C-atoms in the alcohol increases, while a slight dependence on the pH was observed upon changing the acidity of the anolyte solution. In the case of alcohol mixtures, it is the largest alcohol that dictates the overall cell performance

Role of lattice oxygen in the propane combustion over YSZ-supported nanoparticles and films of Pt

International @ AIR+ABO:PVEInternational audienceMetal-Support Interactions (MSI) refers to the effect of the support on the catalytic properties of the supported metal. The phenomenon of Electrochemical Promotion of Catalysis (EPOC) deals with the modification of catalytic activity and selectivity of a catalyst film deposited on a solid electrolyte (ionic conductor) via the application of small electrical potentials or currents. Recent studies on metal-supported catalyst on TiO2 or Yttria-Stabilized Zirconia (YSZ) showed that these two phenomena can be associated with the migration of ionic promoting species containing in the support onto the metallic active sites. These species are responsible for the formation of an effective double layer at the metal-gas interface which affects the binding strength of adsorbed reactants and reaction intermediates. This study reports isotopical labelling experiments during propane oxidation on two different catalytic systems: (a) nanodispersed Pt nanoparticles supported either on ionic conductors (YSZ) or on non-conductive ceramics (ZrO2, SiO2) showing high metallic dispersion and area of triple phase boundary (TPB), (b) Pt catalyst-film deposited on a YSZ membrane (electrochemical catalyst) presenting rather low TPB surface

Role of lattice oxygen in the propane combustion over YSZ-supported nanoparticles and films of Pt

International @ AIR+ABO:PVEInternational audienceMetal-Support Interactions (MSI) refers to the effect of the support on the catalytic properties of the supported metal. The phenomenon of Electrochemical Promotion of Catalysis (EPOC) deals with the modification of catalytic activity and selectivity of a catalyst film deposited on a solid electrolyte (ionic conductor) via the application of small electrical potentials or currents. Recent studies on metal-supported catalyst on TiO2 or Yttria-Stabilized Zirconia (YSZ) showed that these two phenomena can be associated with the migration of ionic promoting species containing in the support onto the metallic active sites. These species are responsible for the formation of an effective double layer at the metal-gas interface which affects the binding strength of adsorbed reactants and reaction intermediates. This study reports isotopical labelling experiments during propane oxidation on two different catalytic systems: (a) nanodispersed Pt nanoparticles supported either on ionic conductors (YSZ) or on non-conductive ceramics (ZrO2, SiO2) showing high metallic dispersion and area of triple phase boundary (TPB), (b) Pt catalyst-film deposited on a YSZ membrane (electrochemical catalyst) presenting rather low TPB surface

Development of Electrode-Supported Proton Conducting Solid Oxide Cells and their Evaluation as Electrochemical Hydrogen Pumps

Protonic ceramic solid oxide cells (P-SOCs) have gained widespread attention due to their potential for operation in the temperature range of 300–500 °C, which is not only beneficial in terms of material stability but also offers unique possibilities from a thermodynamic point of view to realize a series of reactions. For instance, they are ideal for the production of synthetic fuels by hydrogenation of carbon dioxide and nitrogen, upgradation of hydrocarbons, or dehydrogenation reactions. However, the development of P-SOC is quite challenging because it requires a multifront optimization in terms of material synthesis and fabrication procedures. Herein, we report in detail a method to overcome various fabrication challenges for the development of efficient and robust electrode-supported P-SOCs (Ni-BCZY/BCZY/Ni-BCZY) based on a BaCe0.2Zr0.7Y0.1O3−δ (BCZY271) electrolyte. We examined the effect of pore formers on the porosity of the Ni-BCZY support electrode, various electrolyte deposition techniques (spray, spin, and vacuum-assisted), and thermal treatments for developing robust and flat half-cells. Half-cells containing a thin (10–12 μm) pinhole-free electrolyte layer were completed by a screen-printed Ni-BCZY electrode and evaluated as an electrochemical hydrogen pump to access the functionality. The P-SOCs are found to show a current density ranging from 150 to 525 mA cm–2 at 1 V over an operating temperature range of 350–450 °C. The faradaic efficiency of the P-SOCs as well as their stability were also evaluated