铁系无机材料用于新能源电催化硝酸盐还原制氨

Iron-Based Inorganic Materials for New Energy-Based Electrocatalytic Nitrate-to-Ammonia Reduction Reaction

硝酸盐是一类普遍存在的环境污染物,而其对应的还原态氨却是重要的化工原料和农业肥料。因此,探索将两者直接结合的化学转化具有重大的技术及经济战略意义,尤其是对当今“双碳”战略驱动下的高碳排放合成氨的工艺变革以及氨可能成为下一代载氢燃料。通过电催化技术,将硝酸盐还原合成氨过程与可再生能源电力结合,构建绿色低碳的含氮化学品人工“氮循环”的新循环技术与经济体系,是解决目前合成氨工业对化石能源高度依赖、高碳排放问题以及开发新氢能的有力途径。借鉴传统合成氨催化广泛应用、具有成本优势的铁系催化机制,分别选取单质Fe、Fe_(2)O_(3)和Fe_(3)O_(4)作为电催化材料,探索并揭示电催化硝酸盐还原合成氨催化反应的化学形态。结果表明:在相对于可逆氢电极电势为−0.53~−0.93 V区间内,Fe_(2)O_(3)表现出了最优异的催化活性,其生成氨的法拉第效率(FENH3)最高可达88%,对应的生成氨电流密度(J NH3)为43.1 mA/cm^(2)、氨生成速率(rNH3)为0.20 mmol/(cm^(2)·h)。此外,从控制硝酸盐转化率选择性获得氨和硝酸铵两种不同产物的技术路线,分析对比了相应的用电成本以及产品市场价格,充分说明了路线的经济性,说明铁系无机材料在电催化硝酸盐还原合成氨方面具有非常巨大的市场化潜力。

Nitrate is a kind of widespread environmental pollutants,while its corresponding reduction state,ammonia,is an important chemical raw material and agricultural fertilizer.Therefore,exploring the direct chemical transformation between nitrate and ammonia is of great significance technically and economically,especially for the technological upgrade of the energy-intensive ammonia industry driven by the carbon neutrality target and the possibility of ammonia in being the next generation of hydrogen carrying fuel.Among them,the electrocatalytic technology can combine the nitrate-to-ammonia reduction reaction(NARR)process with renewable electricity,building up a new recycling technology and economic system based on the green and low-carbon artificial“nitrogen cycle”of nitrogen-containing chemicals.Therefore,electrocatalytic NARR is an effective route to resolve the problems of high CO_(2) emission and dependence on fossil energy of ammonia industry.Iron-based inorganic materials have been widely applied in the traditional ammonia industry,which also has a huge cost advantage over other materials.In this paper,metallic Fe,Fe_(2)O_(3) and Fe_(3)O_(4) were employed as catalytic materials to explore the optimal chemical state of iron-based catalysts on electrocatalytic NARR.Typically,in the potential range between−0.53 V to−0.93 V(vs.reversible hydrogen electrode,RHE),Fe_(2)O_(3) exhibited the most excellent catalytic activity,whose Faradaic efficiency toward NH3(FENH3)could reach up to 88%.Moreover,the corresponding partial current density of NH3(JNH3)was 43.1 mA/cm^(2),and the NH3 formation rate(rNH3)was 0.20 mmol/(cm^(2)·h).In addition,technical routes toward NH3 and NH4NO3 products could be switched via controlling nitrate conversion ratio.Comparing the corresponding electricity cost and product market price,it was verified that both routes(especially the NH4NO3 route),were economically feasible and the iron-based inorganic materials have a very huge market potential in electrocatalytic NARR.