Synthesis and characterizations of o-nitrochitosan based biopolymer electrolyte for electrochemical devices

For the past decade, much attention was focused on polysaccharide natural resources for various purposes. Throughout the works, several efforts were reported to prepare new function of chitosan by chemical modifications for renewable energy, such as fuel cell application. This paper focuses on synthesis of the chitosan derivative, namely, O-nitrochitosan which was synthesized at various compositions of sodium hydroxide and reacted with nitric acid fume. Its potential as biopolymer electrolytes was studied. The substitution of nitro group was analyzed by using Attenuated Total Reflectance Fourier Transform Infra-Red (ATR-FTIR) analysis, Nuclear Magnetic Resonance (NMR) and Elemental Analysis (CHNS). The structure was characterized by X-ray Diffraction (XRD) and its thermal properties were examined by using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Whereas, the ionic conductivity of the samples was analyzed by electrochemical impedance spectroscopy (EIS). From the IR spectrum results, the nitro group peaks of O-nitrochitosan, positioned at 1646 and 1355 cm-1, were clearly seen for all pH media. At pH 6, O-nitrochitosan exhibited the highest degree of substitution at 0.74 when analyzed by CHNS analysis and NMR further proved that C-6 of glucosamine ring was shifted to the higher field. However, the thermal stability and glass transition temperatures were decreased with acidic condition. The highest ionic conductivity of O-nitrochitosan was obtained at ~10−6 cm-1. Overall, the electrochemical property of new O-nitrochitosan showed a good improvement as compared to chitosan and other chitosan derivatives. Hence, O-nitrochitosan is a promising biopolymer electrolyte and has the potential to be applied in electrochemical devices.近十年来，多糖类天然资源因多类应用场景受到广泛关注。过往诸多研究均报道了通过化学改性手段制备具备新功能的壳聚糖（chitosan），以应用于燃料电池等可再生能源领域。本研究聚焦于壳聚糖衍生物O-硝基壳聚糖（O-nitrochitosan）的合成：通过调控氢氧化钠的不同配比，使壳聚糖与发烟硝酸反应制备该衍生物，并探究其作为生物聚合物电解质（biopolymer electrolytes）的应用潜力。研究采用衰减全反射傅里叶变换红外光谱（Attenuated Total Reflectance Fourier Transform Infra-Red, ATR-FTIR）、核磁共振波谱（Nuclear Magnetic Resonance, NMR）以及CHNS元素分析，对硝基取代情况进行表征；通过X射线衍射（X-ray Diffraction, XRD）解析其分子结构，并借助差示扫描量热法（differential scanning calorimetry, DSC）与热重分析（thermal gravimetric analysis, TGA）考察其热稳定性能。此外，采用电化学阻抗谱（electrochemical impedance spectroscopy, EIS）测试样品的离子电导率。红外光谱结果显示，O-硝基壳聚糖的硝基特征峰位于1646 cm⁻¹与1355 cm⁻¹处，在所有pH介质中均可清晰观测到。当pH为6时，通过CHNS分析测得O-硝基壳聚糖的取代度最高达0.74；核磁共振波谱进一步证实，葡糖胺环的C-6位点向高场发生位移。但在酸性条件下，样品的热稳定性与玻璃化转变温度均有所降低。O-硝基壳聚糖的最高离子电导率约为10⁻⁶ cm⁻¹。综上，相较于纯壳聚糖及其他壳聚糖衍生物，新型O-硝基壳聚糖的电化学性能得到显著改善。因此，O-硝基壳聚糖是一种极具应用前景的生物聚合物电解质，具备应用于电化学器件的潜力。