3D-printed hierarchical pillar array electrodes for high performance semi-artificial photosynthesis

The re-wiring of photosynthetic bio-machineries to electrodes is a forward-looking semi-artificial route for sustainable bio-electricity and fuel generation. Currently, it is unclear how the bio-material interface can be designed to meet the complex requirements for high bio-photoelectrochemical performance. Here, we developed an aerosol jet printing method for generating hierarchical electrode structures using indium tin oxide nanoparticles. We printed libraries of micropillar array electrodes varying in height and sub-micron surface features and studied the energy/electron transfer processes across the bio-electrode interfaces. When wired to the cyanobacterium Synechocysis sp. PCC 6803, micropillar array electrodes with micro-branches gave rise to substantially enhanced biocatalyst loading, light input, and electron flux output compared to state-of-the-art porous structures of the same height. Micropillar electrodes 600 µm in height reached milestone mediated photocurrent densities of 245 µA cm–2 (the closest thus far to theoretical predictions) and external quantum efficiencies of up to 29%. This study provides a blueprint for bio-hybrid electrode design, and tools for where electrode architecture is vital for performance.