This study explores the synthesis and characterization of proton-conducting polymer electrolyte from cellulose and nanocellulose extracted from coconut shell powder, a sustainable resource in Malaysia. Alkali treatment, bleaching, and acid hydrolysis are used for extraction. Surface modifications through alkalization and esterification produce carboxymethyl cellulose (CMC) and carboxymethyl nanocellulose (CMNC) as polymer hosts. Adding ammonium nitrate (NH ₄NO ₃) develops the polymer electrolyte, which is then analysed. FTIR and NMR confirm successful modifications of cellulose and nanocellulose to CMC and CMNC, respectively. TGA shows CMNC has the lowest thermal stability due to its porous structure. XRD reveals increased amorphous properties in modified cellulose and nanocellulose. FESEM and TEM analysed the surface area and particle size. EIS indicates that the CMC–NH ₄NO ₃ system exhibits higher ionic conductivity than the CMNC–NH ₄NO ₃ system in which it showed 2.87 x 10 ^-1 S∙cm ^-1 for CMC-NH ₄NO ₃ and 2.07 x 10 ^-3 S∙cm ^-1 for CMNC-NH ₄NO ₃ at 30 wt% NH ₄NO ₃. The findings highlight proton-based electrolytes from modified cellulose and nanocellulose from coconut shell waste for clean, sustainable energy storage such as proton batteries.