4.1 Materials
K4[Fe(CN)6], K3[Fe(CN)6], lithium bromide, pyrogallic acid, polyethyleneimine (MW: 70 000, 50% wt/v aqueous solution) and sodium carboxymethylcellulose (600-1000mpa, USP) were purchased from Macklin (Shanghai, China). Acrylamide monomer, ammonium persulfate and N,N′-methylene bisacrylamide were purchased from Aladdin (Shanghai, China). Carbon nanotubes were purchased from XFNANO (Nanjing, China).
4.2 Preparation of PA-PEI-Fe film
Pyrogallic acid (1.5 g) was added to a stirred solution of polyethyleneimine (20 g) in deionized water (100 mL) under an atmosphere of nitrogen. A pre-prepared solution of K4[Fe(CN)6]/K3[Fe(CN)6] (0.1 M) and lithium bromide (10 ml, 5.4 mol L−1) was then added to the resulting brown solution and the two were mixed thoroughly. Finally, the mixture was poured into a square mold and spread into a thin film.
4.3 Preparation of TEH
48 ml of the hydrogel prepolymerization solution contained 7.2 g of acrylamide, 36 mg of ammonium persulfate and 4.8 mg of N, N-methylene bisacrylamide. The hydrogel prepolymerization solution was poured into a mold and heated to 60°C for 30 min to polymerization. Then, place the hydrogel into a mixed solution with K4[Fe(CN)6]/K3[Fe(CN)6] (0.1 M) and lithium bromide (5.4 mol L−1) for 3 days to allow adsorption and formation of TEH.
4.4 Preparation of TEH-CNT
Carbon nanotubes were applied as a photothermal layer on the top surface of the thermoelectric hydrogel (TEH). To establish electrical connectivity, a conductive carbon cloth (8 × 65 mm) was used to connect the upper and lower surfaces of the hydrogel, serving as electrodes. To ensure the device’s integrity, the solar-driven TEH-CNT device was sealed using a DELI vacuum machine and thermoplastic tape.
4.5 Preparation of PTEH-Interlocking
TEH was soaked in PA solution (pyrogallol, 12.6 mg mL−1, polyethyleneimine, 0.2g mL−1) for 10 min, removed and wiped free of residual PA solution. The upper and lower surfaces of the hydrogel were subsequently connected using a conductive carbon cloth (8 × 65 mm) as electrodes. Finally, the solar-driven PTEH-Interlocking was hermetically sealed by a DELI vacuum machine with thermoplastic tape.