Salt‐In‐Wood Piezoelectric Power Generators with Circular Materials Design for High‐Performance Sustainable Energy Harvesting

Abstract The nanowatt‐level power density of current biobased piezoelectric energy harvesters restricts their applicative potential for the efficient conversion of biomechanical energy. A high‐performing, fully renewable piezoelectric device incorporating green piezo‐active Rochelle salt in a laser‐drilled wood template is demonstrated to form ordered crystal pillar arrays by melt crystallization. Investigating the effect of different crystal pillar configurations on the piezoelectric response, a shearing design (45°‐oriented pillars) shows potential of up to 30 V and a current of 4 µA – corresponding to a 10‐fold power increase compared to single‐crystalline Rochelle salt. A concept of direct laser graphitization on the crystal surfaces are demonstrated using a fully renewable ink to create electrodes of low resistance (36 Ω sq −1 ). The entire device can be disassembled, fully recycled, and reused. This nanogenerator outperforms state‐of‐the‐art biobased ones and competes with conventional lead‐based devices in power generation while showing a significantly lower environmental footprint, as indicated by life‐cycle assessment.