The demand for sustainable energy storage materials drives the quest for eco-friendly, cost-effective alternatives to conventional electrodes, which frequently depend on hazardous or non-renewable substances. Hence, metal nanoparticles (Cu, Ni, and CuNi alloy) and their nanocomposites with elastin fibril (EF) and elastin monomer (EM) proteins have been synthesized by the chemical reflux method to explore their suitability for energy storage device applications. Among all the nanoparticle-protein combinations, the Cu-EM nanocomposite-based electrode shows the maximum specific capacitance (88 F g \(^{-1}\) ), areal capacitance (176 mF cm \(^{-2}\) ), and maximum energy density (12 Wh kg \(^{-1}\) ) at the applied scan rate of 10 mV s \(^{-1}\) , according to the cyclic voltammetry results. According to electrochemical impedance spectroscopy, the same nanocomposite showed the least charge transfer resistance (0.9 \(\Omega\) ) and the least solution resistance (0.9 \(\Omega\) ). The cyclic stability performance of the Cu-EM electrode was measured through the galvanostatic charge discharge tests. The device demonstrates excellent capacitance retention of 80.2% after the 8000 \(^{th}\) cycle. Thus, the Cu-EM nanocomposites display the best electrochemical performance among all the synthesized samples. It is inferred that the incorporation of Cu nanoparticles in the composite facilitates a fast electron transfer inside the active material, leading to an enhancement in the specific capacitance. The values of the electrochemical parameters, as exhibited, are acceptable for energy storage devices. The Cu-EM nanocomposites are flexible due to the presence of the protein. Thus, these nanocomposite-based electrodes can find applications in flexible energy storage devices. Furthermore, the synthesized material more closely adheres to cost-effective and environmental requirements.
