Gupta Divyani, Kafle Alankar, Nagaiah Tharamani C
Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar-140001, Punjab.
Faraday Discuss. 2023 Jul 19;243(0):339-353. doi: 10.1039/d2fd00150k.
Ammonia (NH) is the second most produced chemical commodity with a worldwide production of 235 million tonnes in 2019, by virtue of its importance in fertilizer production, energy storage and transportation, and in the production of industrial chemicals. The most frequent method of NH production in large plants (1000 to 1500 t day) is the Haber-Bosch process, which has drawbacks of high greenhouse gas emissions (2.16 tonnes CO per tonne of NH) and high energy consumption (over 30 GJ per tonne of NH) due to high pressure and temperature conditions. For sustainable NH production, we require alternative green routes, wherein the electrochemical route holds huge potential due to reduced energy consumption and plant costs, higher selectivity, lower temperatures and pressures, and small to medium scale utilization of NH. However, there are a number of challenges faced during the same low production rates due to difficult N activation and reduced faradaic efficiency due to competing side reactions in aqueous electrolytes. Therefore, the most crucial aspect of electrochemical ammonia production technology is the design of an electrocatalyst which could activate the strong NN triple bond and effectively suppress the competing hydrogen evolution reaction (HER). In addition, the true NH yield estimation is of major concern due to the presence of possible N-contaminants, which may possibly lead to false estimation or overestimation of NH. In this context, we have synthesized an AgVOPO electrocatalyst with rice-grain like morphology an energy efficient and less time consuming sonochemical method to carry out low temperature NH synthesis in an alkaline electrolyte. The choice of Ag metal and an alkaline environment effectually suppresses the HER and the bimetallic phosphate materials (Ag and V metals) induce high activity during nitrogen reduction, while rigorous analysis for tracing/elimination of N-labile and reducible species is considered for true NH production and assessment.
氨（NH₃）是产量第二高的化工产品，2019年全球产量达2.35亿吨，这得益于其在肥料生产、能量存储与运输以及工业化学品生产中的重要性。大型工厂（1000至1500吨/天）生产NH₃最常用的方法是哈伯-博施法，该方法存在温室气体排放高（每吨NH₃排放2.16吨CO₂）和能源消耗高（每吨NH₃超过30吉焦）的缺点，因为反应需要高温高压条件。为了实现可持续的NH₃生产，我们需要替代的绿色路线，其中电化学路线由于能耗降低、工厂成本降低、选择性更高、温度和压力更低以及NH₃的中小规模利用而具有巨大潜力。然而，在电化学合成氨过程中面临诸多挑战，比如由于氮活化困难导致产率低，以及在水性电解质中存在竞争性副反应致使法拉第效率降低。因此，电化学合成氨技术最关键的方面是设计一种电催化剂，该电催化剂能够活化强的N≡N三键并有效抑制竞争性析氢反应（HER）。此外，由于可能存在氮污染物，真实的NH₃产率估算备受关注，这些污染物可能导致对NH₃的错误估算或高估。在此背景下，我们通过一种节能且耗时少的声化学方法合成了具有米粒状形貌的AgVOPO₄电催化剂，用于在碱性电解质中进行低温NH₃合成。选择银金属和碱性环境有效地抑制了HER，双金属磷酸盐材料（银和钒金属）在氮还原过程中具有高活性，同时为了实现真实的NH₃生产和评估，考虑对不稳定和可还原的含氮物种进行严格分析以追踪/消除它们。
