An electrochemical engineering approach to improvements in the zinc-cerium redox flow battery

The zinc-cerium redox flow battery (RFB) offers a higher open circuit cell potential than all vanadium and zinc-bromine systems and competes in the emerging market of utility-scale storage of renewable energy. Previous work on the Zn-Ce RFB has investigated electrolyte composition, the inhibition of hydrogen evolution at the negative electrode, electrode materials and operational conditions of both divided and undivided laboratory cells. After applying 3D- printing to the development of flow cells and porous electrodes, the present work advances the development of the system by introducing new high surface area porous, platinised titanium (Pt/Ti) electrodes for the cerium positive reaction and by performing electrochemical mass transport studies and surface area determination on these materials, along with the measurement of their hydraulic properties. The reaction environment in the critical positive half-cell of the Zn-Ce battery, which governs the cell potential at increasing operational current densities, is considered from the perspective of electrochemical engineering, in contrast to previous literature. Additionally, the cell potential vs. current density relationship for an ideal Zn-Ce unit cell with planar electrodes was simulated, taking into account the Ohmic and kinetic components of cell potential assuming charge transfer regime. Pt/Ti felt and Pt/Ti micromesh electrodes for cerium conversion were electroplated in a flowing alkaline solution. The morphology and distribution of platinum were studied by SEM, EDS and X-ray computed tomography. The volumetric mass transport coefficient of these porous electrodes was determined by the limiting current method and compared to expanded metal and flat plate electrodes. This volumetric mass transport coefficient was found to be more than two orders of magnitude higher with a Pt/Ti felt compared to the planar electrode, yielding a limiting current up to 160 times higher. The pressure drop at the Pt/Ti porous electrodes was higher in those materials with larger surface areas and smaller pore sizes. A pathway for future research and scale-up is discussed