Abstract
Miniaturized cells can be used in photo-electrochemistry to perform water splitting. The geometry, process variables and removal of oxygen bubbles in these cells need to be optimized. Bubbles tend to remain attached to the catalytic surface, thus blocking the reaction, and they therefore need to be dragged out of the cell. Computational Fluid Dynamics simulations have been carried out to assess the design of miniaturized cells and their results have been compared with experimental results. It has been found that low liquid inlet velocities (~0.1 m/s) favor the homogeneous distribution of the flow. Moderate velocities (0.5–1 m/s) favor preferred paths. High velocities (~2 m/s) lead to turbulent behavior of the flow, but avoid bubble coalescence and help to drag the bubbles. Gravity has a limited effect at this velocity. Finally, channeled cells have also been analyzed and they allow a good flow distribution, but part of the catalytic area could be lost. The here presented results can be used as guidelines for the optimum design of photocatalytic cells for the water splitting reaction for the production of solar fuels, such as H2 or other CO2 reduction products (i.e., CO, CH4, among others).
Highlights
The production and storage of energy obtained from renewable sources, the reduction of CO2 emissions into the atmosphere and its re-use are currently some of the main challenges for mankind.Artificial photosynthesis has been used in attempts to mimic the natural water splitting process and to use of the sunlight as an energy source to produce molecules that can be used as feedstock and for energy storage [1,2]
The purpose purpose of of this this study study was was to to establish establish which which hydrodynamic hydrodynamic conditions conditions favor favor aa homogeneous homogeneous
CFD simulations have been used to assess the process design and cell configuration of a photo-electrochemical (PEC) cell in which water is split into protons and oxygen on a catalytic surface
Summary
The production and storage of energy obtained from renewable sources, the reduction of CO2 emissions into the atmosphere and its re-use are currently some of the main challenges for mankind. As far as PEC reactors are concerned, two-compartment PEC cells are generally preferred, from both the cost and safety viewpoints In such a system, the O2 , produced through water oxidation at the anode, is separated directly from the reduction products (i.e., H2 , CO, etc.) that form at the cathode, due to the presence of a proton exchange membrane (PEM), which is used for both H+ transport and to separate the anodic and cathodic chambers. Theoretical models have been developed to analyze the formation and accumulation of bubbles on BiVO4 porous photocatalyst and Pt catalyst surfaces, and their influence on the photoelectric response (as a consequence of the O2 and H2 production rates) for different applied potentials under dark and light conditions [22,23] In one of these models, which employs a percolation approach, it was shown that the photocurrent density decreases over the time due to bubbles generation, under static flow conditions at a fixed applied bias [22]. CFD simulations have been carried out to assess the most efficient design of a microfluidic PEC cell
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