A Janus gold nanowire electrode for stretchable micro-supercapacitors with distinct capacitances

Micro-supercapacitors (MSCs) have drawn tremendous attention in the past several years because of their applications in powering microelectronic systems. Typically, bulk metals or carbon nanomaterials are used for MSC electrodes, but either side of most of these electrodes possesses the same isotropic structure. Here, we report on stretchable MSCs based on patterned enokitake-like vertical gold nanowires (v-AuNWs). Different from previous MSC electrodes, the Janus v-AuNWs can have their "enokitake head" or "enokitake tail" exposed to the electrolyte, leading to a head-exposed MSC (H-MSC) and a tail-exposed MSC (T-MSC), respectively. The H-MSC reveals higher capacitance at a low scan rate but experiences an obvious decrease with increasing scan rate, due to better conductivity of closely packed gold nanoparticles but less ideal ion accumulation/penetration. In contrast, the T-MSC with a separate nanowire structure which is favorable for ion accumulation/penetration, exhibits a perfect rectangular-shaped cyclic voltammetry curve with superior rate capability and cycling stability, and is also able to function under 110% strain with negligible deterioration. Further electrodeposition of polyaniline could enhance the specific capacitance to 5.03 mF cm^-2. The facile fabrication also reduces the complexity of preparation procedures compared to previous extrinsically stretchable designs. These results demonstrate that our Janus enokitake-like v-AuNWs hold great potential in building future soft, stretchable microelectronics.