木质素是自然界中唯一具有芳环结构的天然生物聚合物，是生产能源和芳香化学品的重要可再生原料。木质素氧化解聚制备芳香醛是其增值利用的重要途径之一。传统化学氧化解聚通常需要高温高压等苛刻条件，容易造成产物的过度氧化。此外，由于解聚产物种类繁多，难以通过常规的分离手段有效地分离出芳香醛。因此，亟需开发温和条件下木质素氧化解聚制备芳香醛的新技术和解聚产物综合利用的新方法。本论文将直接木质素燃料电池转换为灵活可控的反应器，通过构建人工电子传递链，促进木质素到氧气的电子传递，实现了温和条件下木质素的氧化解聚制备芳香醛。针对解聚产物难以分离的问题，提出了将解聚产物进行整体衍生化处理的新思路，开发出木质素基抗氧化剂新产品，实现解聚产物的增值利用。首先，通过在泡沫镍（NF）上电沉积金属Co制备了lc-CoSx@NF阳极，使用(VO2)2SO4作为阴极电子介体，开发了高效的直接木质素燃料电池，实现木质素转化为电能的同时在温和的条件下将木质素可控地氧化解聚获得芳香醛产品。在最优条件下电池的峰值功率密度达到199.8 mW·cm-2。芳香醛的收率可通过阳极催化剂和阴极氧化剂筛选、外接负载的调节来便捷地调控，芳香醛最高收率达到7.8%。其次，采用大电流密度的电沉积方法制备了高效的双功能电催化剂hc-CoSx@NF，既可作为阳极催化木质素的电氧化解聚，还可作为阴极催化析氢反应。hc-CoSx@NF电极还可作为直接木质素燃料电池的阳极，90 ℃下电池的峰值功率密度达196.1 mW·cm-2。进一步构建了自供电的木质素氧化解聚与氢气联产的耦合系统，直接木质素燃料电池阳极的总芳香醛收率为2.90%，电解池阳极的总芳香醛收率为3.34%，同时电解池阴极上的氢气产量为12.7 mL H2·cm-2。最后，提出了一种利用羟醛缩合反应对解聚产物进行衍生化处理以提高其抗氧化性的策略，获得了木质素基抗氧化剂新产品。羟醛缩合反应可在芳香醛侧链生成烯酮结构，从而提高抗氧化能力。进一步研究了三种代表性芳香醛单体（对羟基苯甲醛、香草醛和丁香醛）分别与甲乙酮（MEK）进行羟醛缩合，获得了HPPEO、HMPPEO和HDMPPEO三种芳香醛基抗氧化剂，其中丁香醛缩合产物（HDMPPEO）表现出最好的抗氧化能力。结合密度泛函理论（DFT）计算解析了所制备的抗氧化剂的抗氧化机理和构效关系，发现羟醛缩合反应形成的烯酮侧链结构能够降低酚羟基脱氢键解离能（BDE）、电离势（IPo）和电子转移焓（ETE），从而增强了抗氧化能力。苯环上引入甲氧基等给电子基团也能显著提高抗氧

Lignin is a natural biopolymer with phenolic macromolecular structure. It is an important renewable feedstock for production of energy and aromatic chemicals. The oxidative depolymerization of lignin to produce aromatic aldehydes is one of the primary approaches for production of high value-added products from lignin. Traditional chemical oxidative depolymerization usually requires harsh conditions such as high temperature and high pressure, which can easily cause excessive oxidation of the product. In addition, due to complicated compositions of depolymerized products, it is difficult to effectively separate aromatic aldehydes through conventional separation techniques. Therefore, it is imperative to develop new technologies for the oxidative depolymerization of lignin to produce aromatic aldehydes under mild conditions and create new derivative products for integrated utilization of the depolymerized products mixture. In this study, direct lignin fuel cells (DLFCs) were converted to flexible and controllable reactors to produce aromatic aldehydes coupled with electricity generation. By constructing artificial electron transport chains to promote the electron transfer from lignin to oxygen, oxidative depolymerization of lignin to produce aromatic aldehydes was achieved under mild conditions. Considering the difficulty of separating depolymerized products, a new strategy for direct use of the depolymerized products mixture was proposed, and new lignin-based antioxidants were developed to achieve production of value-added products.Firstly, lc-CoSx@NF anode was prepared by electrodepositing Co on nickel foam (NF). With (VO2)2SO4 as the cathode electron mediator, an efficient direct lignin fuel cell was developed to convert lignin into electricity. Simultaneously, aromatic aldehyde products could be obtained by controlled oxidative depolymerization of lignin under mild conditions. Under the optimal conditions, a maximal peak power density of 199.8 mW·cm-2 was achieved. The yield of aromatic aldehydes could be easily controlled by screening the anode catalyst and cathode oxidants as well as simply adjusting the external load. The highest yield of aromatic aldehydes reached 7.8%. Secondly, an efficient bifunctional electrocatalyst hc-CoSx@NF was prepared using a high-current-density electrodeposition method, which could be used as an anode to catalyze the electrooxidative depolymerization of lignin and as a cathode to catalyze the hydrogen evolution reaction (HER). The hc-CoSx@NF electrode could also be used as the anode of a direct lignin fuel cell for converting lignin to electricity, with a peak power density of 196.1 mW·cm-2 at 90 ℃. A self-powered coupled system for oxidative depolymerization of lignin and hydrogen production was further constructed. The total aromatic aldehyde yield at the anode of the direct lignin fuel cell was 2.90%, and that at the anode of the electrolytic cell was 3.34%, while the hydrogen productivity at the cathode of the electrolytic cell was 12.7 mL H2·cm-2. Thirdly, a strategy was proposed to improve the antioxidant properties of the depolymerized products mixture by derivative modification via aldol condensation reactions, and novel lignin-based antioxidants were obtained. A ketene structure on the aromatic aldehyde side chain was generated via the aldol condensation reaction, thereby improving the antioxidant properties. Furthermore, the aldol condensation reaction of three representative aromatic aldehyde monomers (p-hydroxybenzaldehyde, vanillin and syringaldehyde) with methyl ethyl ketone (MEK) was carried out, respectively, resulting in preparation of three aromatic aldehyde-based antioxidants HPPEO, HMPPEO and HDMPPEO, among which the condensation product of syringaldehyde (HDMPPEO) showed the best antioxidant properties. Density functional theory (DFT) calculations was employed to interpret the antioxidation mechanism and structure-activity relationship of the prepared antioxidants. It was found that the ketene side chain structure formed by the aldol condensation reaction could reduce the dehydrogenation bond dissociation energy (BDE), ionization potential (IPo) and electron transfer enthalpy (ETE) of the phenolic hydroxyl group, thereby enhancing antioxidation properties. The introduction of electron-donating groups such as methoxyl group into the benzene ring could also significantly improve the antioxidation properties.