(a) preparing cotton rag nanocellulose (CNF) by treating cleaned cotton rag pieces with 10% sodium hydroxide solution followed by deionized water [DI], bleaching the cotton rag with acetate buffer and 1.5 wt % sodium hypochlorite, followed by refining to a fine pulp using valley beater, followed by grinding in an ultrafriction microgrinder to obtain cotton rag nanocellulose;

(b) preparing polydopamine (PDA) by dispersing dopamine hydrochloride monomer 0.5-2 mg/mL in tris-buffer solution under stirring at 70-90° C. for 20-30 hr and lyophilizing to obtain polydopamine (PDA);

(c) preparing polydopamine coated nanocellulose (PNC) by dispersing 2 mg/mL cotton rag nanocellulose (CNF) as prepared by (a) in tris-buffer solution of pH 8.5 under stirring for 10 hours to 12 hours at 25° C. at a speed of 500 rpm and bath sonication for 15 minutes to 20 minutes to obtain a dispersed nanocellulose solution; followed by adding dopamine hydrochloride monomer into the dispersed nanocellulose solution in a ratio of dopamine to nanocellulose from 1:4 to 1:1 and stirring at 70° C. to 90° C. for 20 hours to 30 hours, followed by lyophilizing to obtain polydopamine coated nanocellulose (PNC);

(d) preparing Nafion solution by cutting Nafion membranes into small pieces and dissolving in a 24:1 (v/v) mixture of isopropyl alcohol and ethyl alcohol by stirring at a temperature from 25° C. to 30° C. and at a speed of 500 rpm;

(e) preparing a homogeneous dispersion of CNF or PDA or PNCs as obtained from (a), (b), and (c) by stirring and sonicating in a 24:1 (v/v) mixture of isopropyl alcohol and ethyl alcohol by stirring at a temperature from 25° C. to 30° C. and at a speed of 500 rpm with periodic bath sonication for 2 hours to 3 hours followed by adding pre-dispersed CNF or PDA or PNC solution into pre-dissolved Nafion solution as obtained from (d) and mixing well by vortex mixing and stirring at 30° C. temperature and at a speed of 500 rpm, degassing the solution and casting in a glass petri dish to afford a 3 wt % CNF/Nafion membrane or a 3 wt % PDA/Nafion membrane or a 3 wt % PNC/Nafion membrane, wherein all the membranes at dry conditions have a thickness of 40 μm to 55 μm when measured at five random locations.