Bifunctional earth-abundant phosphate/phosphide catalysts prepared via atomic layer deposition for electrocatalytic water splitting

The development of active and stable earth-abundant catalysts for hydrogen and oxygen evolution is one of the requirements for successful production of solar fuels. Atomic Layer Deposition (ALD) is a proven technique for conformal coating of structured (photo)electrode surfaces with such electrocatalyst materials. Here, we show that ALD can be used for the deposition of iron and cobalt phosphate electrocatalysts. A PE-ALD process was developed to obtain cobalt phosphate films without the need for a phosphidation step. The cobalt phosphate material acts as a bifunctional catalyst, able to also perform hydrogen evolution after either a thermal or electrochemical reduction step

Combined Experimental-Numerical Analysis of Transient Phenomena in a Photoelectrochemical Water Splitting Cell

A combined experimental-numerical approach was used to study transient phenomena occurring in a photoelectrochemical cell using a membrane-separated porous TiO2-based photoanode and a dark Pt-based cathode. The effects of three parameters (pH in the anodic compartment, operating cell temperature, and cathode compartment preconditioning with hydrogen) on the photocurrent was systematically investigated using design of experiments and analysis of variance. A theoretical model was developed able to accurately reproduce and predict the measurements. The model indicated that the electrochemical reaction uses two parallel pathways on the anodic interface. The first pathway represented the rapid charging of surface states and the subsequent formation of acidic titanol groups at the TiO2/H2O interface which, upon illumination, caused an anodic overshoot at a short timescale. These states recombined with the formed O2 at a longer timescale which resulted in a current decrease after the overshoot. The second pathway was governed by transfer processes of H+ ions at the TiO2/Nafion® interface and caused the observed current increase under illumination and positive relaxation in the dark, both at long timescales. A negative undershoot was observed when the reverse electrolysis reaction was preferred

Monolithic Cells for Solar Fuels.

A tutorial review explaining the many processes occurring in photoelectrochemical cells for solar fuel production, and prospects for future developments

A two-compartment photoelectrochemical cell for solar hydrogen production

In the near future, we need new, clean fuels and alternative sources of hydrocarbons for chemical synthesis. We are investigating a device to directly convert solar light into chemical energy. For this purpose, many materials have already been proposed recently. However, currently very little research has been devoted to the integration of these materials into a working device that outputs separated streams of hydrogen and oxygen. We have designed a fuel cell-like, two-compartment photoelectrochemical cell to enhance efficiency by optimizing transport of reagents and intermediates and by minimizing electrical losses. At the photoanode side, TiO2 absorbs light and uses that energy to split water into oxygen and protons while generating electrons. The protons are transported through a membrane to the other compartment, while electrons pass via an external circuit. At that side, electrons and protons are combined to hydrogen gas on a platinum catalyst. In such a system, each reaction compartment can be optimized independently. First, rate-limiting factors were determined by monitoring photocurrents under a variety of conditions. Besides the water splitting reaction, proton transport was identified as a critical factor and product accumulation at either side was detrimental for long-term performance. This insight was already used to improve performance with modified materials. Implementation of advanced materials could increase efficiencies of this device to a practical level.Was awarded the prize for best oral presentationstatus: publishe

A two-compartment photoelectrochemical cell for hydrogen production

Was awarded the best poster prizestatus: publishe

Design of compact photoelectrochemical cells for water splitting

Solar driven water splitting can be achieved by coupling electrolyzers with PhotoVoltaics (PV). Integration of both functions in a compact PhotoElectroChemical (PEC) cell is an attractive option but presents significant scientific challenges. In this work, the design of single- and dual-compartment PEC cells for research purposes is discussed. The fabrication of separator-electrode assemblies is an important aspect, and upscaling of these architectures even to centimeter scale is not trivial. The layout of a new dual-compartment compact PEC cell with in-situ monitoring of pH, temperatures, and oxygen and hydrogen evolution for research purposes is presented. Finally, a prospect of future PEC cells for practical applications is presented.status: publishe

Interfacial Water Drives Improved Proton Transport in Siliceous Nanocomposite Nafion Thin Films

Nafion proton exchange membranes dehydrate when they are used in the gas phase and in high-temperature applications, such as fuel cells and (photo)electrolysis. Retaining a high level of membrane hydration under such conditions can be achieved by using inorganic fillers, but has never been demonstrated for thin films. Herein, several types of siliceous nanoparticles were incorporated for the first time into Nafion thin films. For composite Nafion materials, increased water uptake does not always induce increased proton conductivity. Here, increased water uptake did result in higher proton conductivity due to a synergistic effect within the composite film. The nanocomposites displayed a higher water uptake than could be expected based on the water uptake of the individual materials. Excess water present at the Nafion-filler interface was found to cause the proton conductivity of nanocomposite Nafion/Ludox AS-40 thin films to double compared with pristine Nafion at low relative humidity (from 2 to 4 mS cm-2 ). Knowledge about the properties of such interfaces will allow for the better design of self-humidifying nanocomposite Nafion membranes, films, and catalyst layers.status: publishe

Chronoamperometric study of membrane electrode assembly operation in continuous flow photoelectrochemical water splitting

Water splitting was performed in a photoelectrochemical cell (PEC) with water oxidation and hydrogen formation reactions in two separate compartments. A photoanode consisting of carbon paper loaded with TiO2 and a cathode made of Pt dispersed on carbon black spread also on carbon paper were fixed on both sides of a Nafion membrane and electrically coupled via an external circuit. Anode and cathode compartments with serpentine flow field were operated either in liquid or vapor phase. Electrical current was monitored with chronoamperometry and D2 formation from deuterated water using mass spectrometry. Mapping the photocurrent under a variety of reaction conditions enabled identification of the limiting factors related to proton and photocarrier transport and reaction product evacuation. This comprehensive research approach to the operation of a PEC will assist future optimization of cell design and development of membrane electrode assemblies.http://pubs.rsc.org/en/content/articlelanding/2013/cp/c3cp50890kstatus: publishe

Combined Experimental-Numerical Analysis of Transient Phenomena in a Photoelectrochemical Water Splitting Cell

© 2016 American Chemical Society. A combined experimental-numerical approach was used to study transient phenomena occurring in a photoelectrochemical cell using a membrane-separated porous TiO2-based photoanode and a dark Pt-based cathode. The effects of three parameters (pH in the anodic compartment, operating cell temperature, and cathode compartment preconditioning with hydrogen) on the photocurrent was systematically investigated using design of experiments and analysis of variance. A theoretical model was developed able to accurately reproduce and predict the measurements. The model indicated that the electrochemical reaction uses two parallel pathways on the anodic interface. The first pathway represented the rapid charging of surface states and the subsequent formation of acidic titanol groups at the TiO2/H2O interface which, upon illumination, caused an anodic overshoot at a short time scale. These states recombined with the formed O2 at a longer time scale which resulted in a current decrease after the overshoot. The second pathway was governed by transfer processes of H+ ions at the TiO2/Nafion interface and caused the observed current increase under illumination and positive relaxation in the dark, both at long time scales. A negative undershoot was observed when the reverse electrolysis reaction was preferred.status: publishe