Soft gold nanowire sponges for strain-insensitive conductors, wearable energy storage and catalytic converters

Electronics is evolving from rigid, flexible to ultimate stretchable electronics, in which active optoelectronic materials are required to be deposited onto or embedded into elastomeric materials. We have recently demonstrated a powerful solution-based electroless gold coating technology, which enables the growth of enokitake-like gold nanowires on two-dimensional elastomeric sheets and one-dimensional fibers for a wide range of applications in wearable bioelectronics. Here, we show that such an elastomeric gold coating technology can be extended to three-dimensional (3D) elastomeric sponges. We have successfully grown vertically-aligned enokitake-like gold nanowires (v-AuNWs) uniformly throughout 3D sponge skeletons, leading to a highly conductive sponge with a conductivity of up to about 1500 S m-1. This, in conjunction with embedment of Ecoflex into porous v-AuNW sponge, led to a strain-insensitive conductor that only changed about 17.3% in resistance under 50% strain, and 83.3% in resistance under 100% strain. The conductor could be stretched up to ∼340% strain before losing its conductivity. Furthermore, the strain-insensitive sponge conductors were used as electrodes to fabricate elastic supercapacitors, which could retain 102% and 99% of initial capacitance under 50% compression strain and 180° bending, respectively. In addition, our gold sponge was also catalytically active, and could serve as a recyclable 3D porous catalyst (achieving 90% conversion efficiency even after 10 cycles of 4-nitrophenol reduction reaction). The results presented here demonstrate a simple yet efficient wet chemical approach to a multifunctional sponge for applications in stretchable electronics, wearable energy devices and catalysis.