微藻提油残渣可控制备氮掺杂生物炭材料及其催化氧还原机理

Nitrogen-doped carbon-based materials are widely used in catalyzing oxygen reduction reaction (ORR) due to their high electron conductivity, cost-effectiveness, high stability. However, the introduction of exogenous nitrogen is complex and expensive. In this project, the controllable synthesis of in-situ nitrogen-doped biomass carbon has been achieved by adjusting the synthesis conditions with microalgae residual biomass after oil extraction as precursor, and the effects of preparation factors on its structure, component, nitrogen forms are also been studied with the purpose of revealing carbonation mechanism and pore forming mechanism. The effect of nitrogen-doping and pore structure on the ORR catalytic activity has also been investigated accompanied by the reaction kinetics of ORR, then the mechanism of nitrogen doping on the biomass carbon towards ORR will also be clarified. Thus, the efficient development of microbial fuel cells and resource utilization of microalgae extraction residue will also be achieved. This type of catalysts can be also applied to other air cathode batteries (including proton exchange membrane fuel cells and direct formic acid fuel cells, etc.), which can significantly reduce the electrode cost. The design concept developed here opens up a new avenue for constructing nitrogen-doped carbon materials with improved electrochemical activity and high stability. The achievements from this project provide a novel design strategy to the resource utilization of nitrogen-rich biomass materials.

氮改性炭材料因其来源广，价格便宜，稳定性能好，在催化氧还原领域应用广泛，但外源氮引入工艺复杂，成本高，本项目以富氮生物质废弃物-微藻提油残渣为前驱体，通过调控制备条件，实现原位氮掺杂炭材料的可控合成，明晰微藻提油残渣碳化机理和成孔机制，研究掺杂氮形态和孔结构对生物炭基催化剂的氧还原活性影响规律，结合动力学测试，揭示掺杂氮形态对生物炭材料催化氧还原反应的作用机制，为兼具高催化活性和高稳定性的氮掺杂炭材料催化剂的原位可控合成提供了新思路、新方法；为降低空气阴极电池（如微生物燃料电池和质子交换膜燃料电池等）电极成本提供新路径；为富含氮类生物质原料高效资源化利用提供技术指导和理论基础。

氮掺杂生物炭由于成本低、结构可调控、稳定性能好等特点在催化氧还原反应（oxygen reduction reaction，ORR）领域应用广泛。但其制备过程中氮转化规律不明晰，氮流失或不可控转化会造成掺杂量不足，针对此，本项目以微藻提油残渣为原料，采用一步热解法制备生物炭，通过研究提油预处理、热解温度和升温速度等工艺，解析其对生物炭材料结构、形貌及N含量、形态的影响规律，实现微藻生物质热解过程中氮转化调控。进一步结合电催化测试，分析掺杂氮对ORR的作用规律，解析氮掺杂耦合孔结构调控对ORR反应的作用机理。.研究表明提油预处理使残渣的氮含量提升了3.69 at. %，富氮效果明显，同时还能疏松原料结构，改善热解产物孔结构和比表面积。热解温度，升温速率等热解工艺对催化剂结构、形貌以及氮含量和氮形态都有影响，随温度升高，吡咯氮、吡啶氮和石墨氮会相互转变，石墨氮热稳定性最大，同时热解过程中的气体产物也能促进炭材料的二次活化，优化炭材料的结构和氮掺杂, 结合热解机理分析，提出了 “梯度升温”热解方式，实现了微藻热解过程中“富氮-保氮-控氮”调控。进一步电化学测试表明：吡啶氮和石墨氮有助于促进ORR理想的4e-途径的选择性，吡咯氮可促进2e-途径，优化后的生物炭ORR起始还原电位达到0.223 V，负载该催化剂的微生物燃料电池最大输出电压为561 mV，最大功率密度达到843.6 mW m-2，实现了炭基ORR催化剂的高效开发和微藻残渣资源化利用。 .研究工作共发表论文7篇，申请专利4项，在本项目研究工作基础上，本人获得国家自然科学基金—面上项目：（52176214）和中国科学院青年创新促进会人才项目（2020345）的资助。..