An integrated battery-electrolyzer stores renewable electricity as a battery and produces hydrogen when overcharged. This dual application requires electrode concepts that ideally enhance both battery and electrolysis operation without compromising either. One such concept is 3D structured electrodes including channels that improve ionic conductivity and material utilization as well as facilitating bubble removal during electrolysis. In this work, we first develop a 1D model of a porous sintered nickel electrode that takes the void fraction of the 3D geometry into account and allows for the determination of the current and potential distribution for both battery charging and oxygen evolution. An optimized void fraction that maximizes the reactive surface area for oxygen evolution is determined, and we discuss under what circumstances a 3D geometry is beneficial. Finally, we show how the improved ionic conductivity of 3D electrodes also results in more homogeneous battery charging, increasing charging efficiency in nickel electrodes.

A renewable power-based energy system will require both short- and long-term electricity storage and conversion to hydrogen-based fuels. This study investigates 3D electrodes for an integrated alkaline Ni-Fe battery and electrolyzer. The dual system can sustain current densities similar to those in alkaline electrolyzers while simultaneously reaching efficient hour-duration battery-storage capacities. We demonstrate that the combination of microporosity and a conductive three-dimensional (3D) electrode design with macroscopic channels enables the required current densities during charge, electrolysis, and discharge. The ionic conduction in the 3D electrode enables higher utilization of the active electrode mass and lower overpotentials during both the (dis)charge reaction and electrolysis. The double function of these electrodes is understood from a general statistical model and a more detailed porous-electrode model perspective. The 3D structuring provides a pathway forward, accessible with industrially established techniques, to these higher-power and higher-energy-density electrodes.

Molecular catalysts play a significant role in chemical transformations, utilizing changes in redox states to facilitate reactions. To date molecular electrocatalysts have efficiently produced single-carbon products from CO2 but have struggled to achieve a carbon–carbon coupling step. Conversely, copper catalysts can enable carbon–carbon coupling, but lead to broad C2+ product spectra. Here we subvert the traditional redox-mediated reaction mechanisms of organometallic compounds through a heterogeneous nickel-supported iron tetraphenylporphyrin electrocatalyst, facilitating electrochemical carbon–carbon coupling to produce ethanol. This represents a marked behavioural shift compared with carbon-supported metalloporphyrins. Extending the approach to a three-dimensional porous nickel support with adsorbed iron tetraphenylporphyrin, we attain ethanol Faradaic efficiencies of 68% ± 3.2% at −0.3 V versus a reversible hydrogen electrode (pH 7.7) with partial ethanol current densities of −21 mA cm−2. Separately we demonstrate maintained ethanol production over 60 h of operation. Further consideration of the wide parameter space of molecular catalyst and metal electrodes shows promise for additional chemistries and achievable metrics.