气体扩散电极电化学非均相催化氧化气态单质汞的研究

The removal of Hg0 in the coal-fired flue gas is difficult. Adsorption is effective but expensive, while chemical oxidation requires the addition of lots of oxidants. In this study, an electrochemical method using GDE is proposed to oxidize Hg0 to Hg2+ using a large number of high-energy oxidizing species generated on the electrode surface. The research contents include: (1) Development of the highly catalytic GDE. Screen highly catalytic components with O2 great adsorption coefficient under lean O2 and under acidic condition, employ active carbon fiber as the electrode substrate, and prepare dimensionally stable GDE with improved catalytic performance by impregnation and drying process; (2) Explore the Hg0 oxidation mechanism and the electrochemical behavior of Hg2+ generated. Use Tafel, CV, EIS to obtain the complex impedance and Bode diagram, together with the reaction characterization and the dynamic information of electron transfer and contaminant transformation, thereby enhancing the electrochemical process to ensure efficient Hg0 oxidation in the flue gas; (3) Clarify the mass transfer of Hg0 and O2 in a three-phase catalytic process through the waterproof breathable layer and the thin liquid film to the electrode surface. Optimize the structure of the electrode substrate to reduce the stationary liquid film thickness on electrode surface, and to improve the mass transfer coefficient of Hg0 and O2, thereby reducing concentration polarization, and enhancing the yield of the oxidized species. Ultimately, achieve highly efficient Hg0 oxidation with low energy consumption.

零价汞的脱除是燃煤烟气脱汞的难点。吸附法脱汞效果好但费用高，化学氧化法需添加大量氧化剂。本研究提出GDE非均相氧化法，利用其表面电化学产生的大量高能量氧化物种在气液界面将零价汞氧化为Hg2+脱除！内容包括：1）高催化活性GDE电极研发。筛选贫氧条件下对O2吸附系数大及酸性条件下催化氧化性高的复合组分，以ACF为电极基体，通过浸渍负载及干燥工艺提升催化层活性；2）探询零价汞氧化机制及产生Hg2+的电化学行为。通过Tafel、CV、EIS等监测并结合反应过程解析电子传递和污染物转移动态信息，增强电化学过程保障烟气中零价汞的高效氧化；3）明晰三相催化过程中零价汞和O2通过防水透气层、薄液膜穿过电极的传质过程。通过优化电极基体空间结构降低表面有效静止液膜厚度、提高传质系数，由此降低气体传质阻力及浓差极化、提升氧化物种产率，达到高效、低能耗氧化零价汞的目的。

零价汞（Hg0）是燃煤烟气中汞的主要存在形式之一，目前燃煤烟气脱汞技术的重点和难点在于如何提高烟气中零价汞的转化率，即如何高效地将燃煤烟气中的气态零价汞转化为氧化态汞。由于气体扩散电极的原位产H2O2技术及电极的三维多孔结构能提供大量气液固三相接触面，能够保证较高的氧传质系数和氧还原（ORR）效率，已成为水处理高级氧化技术的研究热点。在此基础之上，创新提出将高效产H2O2气体扩散电极应用于燃煤烟气中零价汞（Hg0）的电化学阴极氧化和阳极氧化研究，以实现零价汞（Hg0）向氧化态汞（Hg2+）的高效转化，并探讨了该工艺的相关调控机制。