以木质纤维素为代表的生物质资源具有产量丰富、碳中性等优点，是生产可再生能源和化学品的重要原料。木质纤维素的生物炼制过程中，纤维素和半纤维素可通过化学或生物方法转化生产多种生物基材料和化学品，而木质素往往作为废弃物处理。木质素结构相对复杂，难以通过简单的化学或生物方法进行转化，但木质素具有较高的热值，可作为清洁燃料用于热能和电能的生产。以木质素为燃料通过燃料电池技术生产电能是一个前沿且具有挑战性的课题。已有的燃料电池技术通常需要额外的预处理将木质素转化为碳、可燃气体或小分子物质才能更好地进行电能生产，而预处理过程会造成显著的?损失。因此，亟需开发温和条件下高效转化木质素生产电能的新技术。本论文在对直接生物质燃料电池原理深入理解的基础上，基于生物体呼吸电子传递链和绿色植物光合电子传递链的仿生思想，构建了人工电子传递链，使用具有合适电极电位梯度的氧化还原电对作为电子载体，逐级介导木质素电子向空气氧的高效传递，开发出温和条件下木质素高效电能转化的直接木质素燃料电池新技术，为木质素的转化提供新思路。 首先，构建了基于可溶性电子载体K3[Fe(CN)6]和(VO2)2SO4的人工电子传递链，实现了温和条件下木质素的高效直接电能转化。阳极电子载体K3[Fe(CN)6]可快速提取木质素中电子，电子提取效率达98%，部分木质素被矿化为CO2。开发了内循环式反应器强化(VO2)2SO4被空气氧化再生，促进电子传递速率，所开发的直接木质素燃料电池的电子传递链整体效率>90%，峰值功率密度达200 mW/cm2。 其次，筛选出CoS作为有效的固态电子载体（电催化剂），开发出以负载CoS的泡沫镍为阳极的直接木质素燃料电池，解决了可溶性电子载体难以分离和回收的问题，电池峰值功率密度达175 mW/cm2，阳极库伦效率达97%。放电过程中木质素β-O-4键发生显著断裂，芳环发生开环反应生成脂肪酸，甚至被矿化为CO2。 最后，扩展了电子传递链的应用，开发了B、O共掺杂的木质素基催化剂，实现以空气为氧源的H2O2高效电化学生产，木质素基碳催化剂的分子选择性>95%，法拉第效率>95%，生成速率达11812 mmol/(g·h)。通过在阳极上耦合木质素的氧化反应取代析氧反应，获得了更高的H2O2生成速率，并使电解能耗降低了11.4%。进一步构建了直接木质素燃料电池（产电）与H2O2电化学生产（用电）的耦联体系，开发出基于木质素电子供给的、空气为廉价氧源的H2O2生产新技术，获得了93.7%的电子传递总效率。

Lignocellulose is a representative biomass resource with the advantages of abundance, carbon neutrality etc. It is one of the most important biomass resources for sustainable production of renewable energy and chemicals. In the biorefining process of lignocellulose, the polysaccharide components, i.e., cellulose and hemicelluloses can be converted to multiple value-added bio-based materials and chemicals through various chemical or biological processes, while lignin is usually treated as wastes. Lignin has relatively complex chemical structure, and is usually difficult to convert by simple chemical or biological ways; however, lignin has relatively high calorific value, making it be a good and clean fuel for heat production and electricity generation. Using lignin as a fuel to generate electricity through fuel cell technologies is an advanced and challenging reasearch topic. Currently, the existing fuel cell technologies usually needs external pretreatment processes to covert lignin to carbon, gaseous fuels or small molecules before feeding the fuel cells for electricity generation, however, external pretreatments usually cause serious loss of exergy. Therefore, it is urgent to develop new technology to convert lignin to electricity under mild conditions. In this study, by in-depth understanding the principle of direct biomass fuel cells and inspiration from the respiration electron transport chain in living organisms and photosynthetic electron transport chain of green plants, artificial electron transport chains were constructed with redox couples as electron carriers to transfer electrons from lignin to air (oxygen) under mild conditions, thus efficiently generating electricity under mild conditions. This novel direct lignin fuel cell technology may provide new idea for lignin conversion and utilization. Firstly, an artificial electron transport chain was constructed with K3[Fe(CN)6] and (VO2)2SO4 as water-soluble anodic and cathodic electron carriers, respectively, which achieved highly-efficient conversion of lignin to electricity under mild conditions. The anode electron carrier, K3[Fe(CN)6] could quickly and efficiently oxidize lignin and extract electrons with 98% electron extraction efficiency. A part of lignin was even mineralized to CO2. An internal recycle reactor was further developed to facilitate the oxidative regeneration of cathodic electron carrier, (VO2)2SO4, by air. About 90% of overall efficiency of electron transfer was achieved by this electron transport chain to convert the chemical energy of lignin to electric energy. Under the optimal operation condition, a maximal peak power density of 200 mW/cm2 was achieved, being the highest among the reported results of various direct biomass fuel cells. Secondly, a novel electron transport chain with insoluble metal sulfides as the anodic electron carriers (electrocatalysts) was developed to achieve direct conversion of lignin to electricity under mild conditions, avoiding the separation problems caused by using soluble electron mediators. CoS was screened as the most efficient anodic electrocatalyst. The direct lignin fuel cell quipped with nickel foam anode loaded with CoS catalyst obtained the highest peak power density of 175 mW/cm2 with an anode current efficiency of 97%. During the discharging process, lignin underwent significant depolymerization and degradation primarily by cleavage of β-O-4 aryl ether bond, while ring-opening reactions also took place to form aliphatic acids, and even a part of lignin was mineralized to CO2. Finally, the electron transport chain was further extendedly applied for electrochemical production of H2O2. A novel B, O co-doped lignin-based carbonous catalyst was developed to catalyze H2O2 production with air as an oxygen source. The prepared catalysts exhibit superior two-electron oxygen reduction reaction (2e- ORR) activity with molecular selectivity of >95%, faradaic efficiency of >95%, and H2O2 production rate of 11812 mmol/(g·h), which is the highest level reported so far. By coupling lignin oxidation instead of oxygen evolution reaction (OER) on the anode with H2O2 production, higher H2O2 production rate was achieved, with the energy consumption of the system being reduced by 11.4%. A coupled system was further developed by combining the direct lignin fuel cell with the electrolytic cell for H2O2 production, which achieved transfer of electrons from lignin to the oxygen of air, resulting in efficient production of H2O2 by using lignin as an electron source. The overall electron transfer efficiency of the coupled system reached 93.7%.