Tobacco mosaic virus-templated hierarchical Ni/NiO with high electrochemical charge storage performances

• 300 °C annealing of Ni-coated TMVs resulted in optimized performance of TMV/Ni-core NiO-shell nanoelectrodes when tested in 2 M KOH.
• Hierarchical-Ni/NiO electrodes are fabricated by combining Au-coated Si micropillar arrays with the TMV/Ni/NiO nanoelectrodes.
• 32.6-fold increase in areal capacity is achieved with hierarchical electrodes (81.4 μAh cm−2) compared to planar electrodes (2.5 μAh cm−2).
• An interesting charge capacity increase phenomena is analyzed by comparing changes in electrochemical performances and electrode morphology.
• Stable galvanostatic charge/discharge at 2 mA cm−2 up to 1500 cycles with no capacity fading.

Three-dimesional hierarchical electrodes exhibiting multi-dimensional geometries provide exceptional advantages for advanced energy storage performance. In this work, we report the fabrication and characterization of biotemplated hierarchical-Ni/NiO electrodes enabled by thermal oxidation of electroless Ni-coated Tobacco mosaic viruses (TMVs) self-assembled on Au-coated Si micropillar arrays. Uniform NiO formation on the metallized TMV nanoscaffolds is characterized by XPS and STEM-EELS analysis and the electrochemical performance was characterized in 2 M KOH solution. The hierarchical-Ni/NiO show a 3.3 and 32.6 times increase in areal capacity (81.4 μAh cm−2) compared to solely nanostructured (24.3 μAh cm−2) and planar electrodes (2.5 μAh cm−2), respectively. The NiO electrodes show interesting capacity increase phenomenon during the initial activation cycles. Based on our experimental analysis, it is attributed to both an increase in active surface area/mesoporosity and NiO content during the initial charge/discharge cycles, and the increase has dependence on electrode geometry. The hierarhical-Ni/NiO electrode exhibit excellent cycle stability up to 1500 charge/discharge cycles at 2 mA cm−2 with no capacity fading. Based on the results, the hierarchical-Ni/NiO is a promising candidate for advanced electrochemical energy storage devices.