Energy storage devices, like redox-flow batteries and redox-supercapacitors, generate electrochemical potential by charging redox-active molecules. A key component in this class of devices is an ion-selective membrane that prevents redox-molecule crossover between half-cells, while allowing small ions to pass with minimal resistance. Conventional membranes often use ‘forever chemicals’ like Per-fluoroalkyl substances (PFAS), impacting their environmental footprint. This work introduces novel manufacturing methods for membranes made from coatings of cellulose nanofibril on kraft paper for use in these devices. The coating process is optimized to block redox-active molecules (e.g., alizarin red s and lignosulfonate) and enhance wet ionic conductivity. By refining the cellulose coating with chemical crosslinkers, leakage of redox molecules is reduced by an order of magnitude compared to uncoated kraft paper, without affecting conductivity. The goal is to pave the way for more environmentally friendly membranes in energy storage electrochemical cells. This innovation not only addresses environmental concerns but also the scalability of manufacturing, while maintaining the efficiency and functionality required for the envisioned applications.