Ligthart Nathalie E G, van Langevelde Phebe H, Padding Johan T, Hetterscheid Dennis G H, Vermaas David A
Department of Chemical Engineering, Delft University of Technology, Van der Maasweg 9, 2629HZ Delft, The Netherlands.
Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands.
ACS Sustain Chem Eng. 2024 Aug 12;12(34):12909-12918. doi: 10.1021/acssuschemeng.4c03919. eCollection 2024 Aug 26.
Electrochemical oxygen reduction is a promising and sustainable alternative to the current industrial production method for hydrogen peroxide (HO), which is a green oxidant in many (emerging) applications in the chemical industry, water treatment, and fuel cells. Low solubility of O in water causes severe mass transfer limitations and loss of HO selectivity at industrially relevant current densities, complicating the development of practical-scale electrochemical HO synthesis systems. We tested a flow-by and flow-through configuration and suspension electrodes in an electrochemical flow cell to investigate the influence of electrode configuration and flow conditions on mass transfer and HO production. We monitored the HO production using Cu-tmpa (tmpa = tris(2-pyridylmethyl)amine) as a homogeneous copper-based catalyst in a pH-neutral phosphate buffer during 1 h of catalysis and estimated the limiting current density from CV scans. We achieve the highest HO production and a 15-20 times higher geometrical limiting current density in the flow-through configuration compared to the flow-by configuration due to the increased surface area and foam structure that improved mass transfer. The activated carbon (AC) material in suspension electrodes, which have an even larger surface area, decomposes all produced HO and proves unsuitable for HO synthesis. Although the mass transfer limitations seem to be alleviated on the microscale in the flow-through system, the high O consumption and HO production cause challenges in maintaining the initially reached current density and Faradaic efficiency (FE). The decreasing ratio between the concentrations of the O and HO in the bulk electrolyte will likely pose a challenge when proceeding to larger systems with longer electrodes. Tuning the reactor design and operating conditions will be essential in maximizing the FE and current density.
电化学氧还原是目前过氧化氢（HO）工业生产方法的一种有前景且可持续的替代方案，过氧化氢在化学工业、水处理和燃料电池等许多（新兴）应用中是一种绿色氧化剂。在工业相关电流密度下，O在水中的低溶解度导致严重的传质限制和HO选择性损失，这使得实用规模的电化学HO合成系统的开发变得复杂。我们在电化学流动池中测试了流通式和贯通式配置以及悬浮电极，以研究电极配置和流动条件对传质和HO生成的影响。在pH中性磷酸盐缓冲液中，我们使用Cu-tmpa（tmpa = 三（2-吡啶甲基）胺）作为均相铜基催化剂，在1小时的催化过程中监测HO的生成，并通过循环伏安扫描估计极限电流密度。与流通式配置相比，贯通式配置中由于表面积增加和泡沫结构改善了传质，我们实现了最高的HO生成量和几何极限电流密度高出15 - 20倍。悬浮电极中的活性炭（AC）材料具有更大的表面积，会分解所有生成的HO，证明不适合用于HO合成。尽管在贯通式系统中微尺度上传质限制似乎有所缓解，但高O消耗和HO生成在维持最初达到的电流密度和法拉第效率（FE）方面带来了挑战。当使用更长电极的更大系统时，本体电解质中O和HO浓度之间不断下降的比例可能会带来挑战。调整反应器设计和操作条件对于最大化FE和电流密度至关重要。
