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Nafion has been dominating the proton exchange membrane (PEM) market because of its adequacy for the proton exchange operation. However, because of its high cost, low performance at low relative humidity, and finally environmental unfriendliness, researchers have been developing and working on Nafion alternatives. In this review, we assess how biopolymers present an opportunity as an eco‐friendly material able to replace the conventional Nafion membrane in proton exchange membrane fuel cells (PEMFC). Chitosan and cellulose were the most studied in literature owing to their abundance in nature, low cost, and high affinity for water, which are sought‐after properties for PEM. In addition to that, their ease of modification through their hydroxyl or amine groups represents an opportunity to further enhance their characteristics and thus meet the criteria of diverse applications. The use of biopolymers as an adequate PEM is facing many challenges. Having a practical proton conductivity and securing the physicochemical stability of the biopolymers in fuel cell operating conditions are two of the most important challenges to overcome. Promising strategies to simultaneously address these challenges such as crosslinking, making interpenetrated networks, and making blends and composites are reported. [ABSTRACT FROM AUTHOR]

Nickel orthophosphate, Ni3(PO4)2, was successfully synthesized using solid‐state reaction at 900 °C. The effect of the calcination temperature on the material purity was investigated at different temperatures (700–900 °C). XRD analysis has shown that Ni3(PO4)2 crystallizes in a monoclinic system with P21/a space group. The electrochemical performances of carbon‐coated Ni3(PO4)2 were investigated for the first time versus Li+/Li and improved by the optimization of the cut‐off voltage, the carbon‐coating source, and the binder used. The best performance was delivered when using 0.01 V cut‐off voltage, sucrose for C‐coating, and carboxymethyl cellulose (CMC) binder. A reversible capacity of 249 mAh g−1 and a capacity retention around 74–79 % after 90 cycles with a good coulombic efficiency of 98 % were obtained at C/5 current rate. In situ XRD measurements demonstrated the irreversible amorphization of the Ni3(PO4)2 crystal structure during the first discharge process, confirming that this phosphate exhibits a pure conversion mechanism. [ABSTRACT FROM AUTHOR]

Pure Li0.8M0.1Ti2(PO4)3 (M: Co, Mg) phosphates with the NASICON‐type structure were synthesized using a solid‐state reaction. Depending on the cation, M, the synthesis temperature and the annealing duration were optimized. The electrochemical performances of Li0.8M0.1Ti2(PO4)3 were evaluated as negative electrode materials for Li‐ion batteries over two different voltage ranges, 1.5–3.0 V and 1.0–3.0 V. The best electrochemical results were obtained for the voltage range 1.5–3.0 V with discharge capacities of 100 mAh g−1 and 80 mAh g−1 for Li0.8Co0.1Ti2(PO4)3 and Li0.8Mg0.1Ti2(PO4)3, respectively, over 20 cycles with capacity retentions exceeding 80 %. Raman spectroscopy was used to confirm the formation of the carbon layer after the carbon‐coating procedure. In operando XRD was performed to investigate the structural changes upon the first discharge/charge cycle, showing the progressive evolution of Li‐poor and Li‐rich phase fractions. Ex situ XPS analysis was conducted to follow the oxidation state of titanium during the insertion/de‐insertion of lithium ions, demonstrating that the redox couple (Ti4+/Ti3+) is reversibly active during the electrochemical cycling. [ABSTRACT FROM AUTHOR]