Cellulose Nanofiber-Supported Electrochemical Percolation of Capacitive Nanomaterials with 0D, 1D, and 2D Structures

Cellulose nanofiber (CNF) represents a promising support material to strengthen the mechanical property of free-standing supercapacitor electrodes comprised of conducting nanomaterials. Although efforts have been focused on improving the performance of the CNF-supported electrode, the percolation of capacitive nanomaterials within the insulating CNF matrix, and its correlation with the nanomaterial's dimensionality are still underexplored. In this work, membrane supercapacitor electrodes are fabricated by incorporating CNF with 0D, 1D, and 2D capacitive nanocarbons respectively to study the impact of their dimensionality. It is found that the percolation pathway of the nanocarbons is dependent on their dimensionality. By introducing a new definition termed as electrochemical percolation threshold, the threshold weight percentages to realize effective electrochemical percolation are determined to be 60.0, 14.3, and 66.7% for 0D, 1D, and 2D nanocarbons, respectively. Increasing the weight percentage beyond the threshold typically results in improved electrochemical percolation but reduced mechanical strength, and both trends are dependent on the nanocarbon's dimensionality. The results provide guidance to design efficient and robust CNF-supported supercapacitor electrodes by controlling the dimensionality and density of the active material. The insights regarding the electrochemical percolation threshold can be applied to other energy-storage nanomaterials to advance the development of insulator-supported supercapacitors.