Effect of gel ageing and electrode corrosion on the performance of direct laser writing carbonization-enabled hydrogel-based moist-electric generators

The combined use of hydrogel active materials and porous and asymmetric electrodes enables the development of high-performance and high-power output moist-electric generators (MEGs). Herein, we report a direct laser writing carbonization (DLWc)-enabled approach for cost-effectively manufacturing the porous carbon electrode that can be easily integrated and assembled with the hydrogel active material for the scalable fabrication of MEGs. With the hydrogel active material composed of poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA), phytic acid (PA), glycerol and water, the best performing DLWc-enabled PVA/PAA/PA hydrogel-based MEG exhibited an open-circuit voltage of ∼0.8 V and a short-circuit current density of ∼110 μA cm^-2 and delivered stable operation for more than 300 h in an ambient environment. In-depth studies further revealed the effect of time-ageing treatment of the hydrogel active material on its ionic conductivity and water uptake ability and the power performance of the finally assembled MEGs. Lastly, the combined investigations using microscopy, spectroscopy and electrochemical corrosion tests allowed us to unambiguously identify the critical roles of the corrosion reaction occurring at the metallic electrodes in enhancing the voltage and current performance of the hydrogel-based MEG.