Print-and-Plate Porous Electrodes for Flow Batteries

Flow batteries contain redox-active species that are stored in the liquid state and pumped through porous electrodes. High-performance electrodes should be designed to limit losses from charge transfer, resistance to electrical conduction, and hydraulic pressure drop. A complex interplay between electrode composition and architecture as well as electrolyte flow dynamics controls their performance. Most flow batteries use porous electrodes composed of randomly oriented (<i>e.g.</i>, electrospun) carbon fibers, whose intrinsically disordered structure makes these important structure-property-performance relationships difficult to elucidate. Here, we report a “print-and-plate” fabrication method to generate conductive electrodes with programmable lattice architectures. Our three-step fabrication process involves: (i) direct ink writing of micro-architected lattices, (ii) electroless nickel plating to enhance conductivity, and (iii) gold electroplating to impart electrochemical stability. The resulting electrode lattices consist of microscale features that exhibit mΩ sq^-1 sheet resistance and sufficient porosity for low pressure drop in flow battery applications. We directly visualize their function in an anthraquinone disulfonate (AQDS) half-cell with chronopotentiometry and in situ fluorescence microscopy. Based on these observations, we then employ inverse design to strategically encode lattice defects (e.g., missing fiber segments) to investigate their effect on performance. Using confocal fluorescence microscopy, we quantitatively mapped the state of charge with sub pore-scale resolution in these print-and-plate electrodes in an operando AQDS half-cell. Our integrated approach for electrode design, fabrication, and testing provides a powerful platform for understanding and improving the performance of porous electrodes in electrochemical flow cells.