Ni-Doped Mo2C Anchored on Graphitized Porous Carbon for Boosting Electrocatalytic N2 Reduction

Nitrogen Electrocatalysis: Electrolyte Engineering Strategies to Boost Faradaic Efficiency

The electrochemical activation of dinitrogen at ambient temperature and pressure for the synthesis of ammonia has drawn increasing attention. The faradaic efficiency (FE) as well as ammonia yield in the electrochemical synthesis is far from reaching the requirement of industrial-scale production. In aqueous electrolytes, the competing electron-consuming hydrogen evolution reaction (HER) and poor solubility of nitrogen are the two major bottlenecks. As the electrochemical reduction of nitrogen involves proton-coupled electron transfer reaction, rationally engineered electrolytes are required to boost FE and ammonia yield. In this Review, we comprehensively summarize various electrolyte engineering strategies to boost the FE in aqueous and non-aqueous medium and suggest possible approaches to further improve the performance. In aqueous medium, the performance can be improved by altering the electrolyte pH, transport velocity of protons, and water activity. Other strategies involve the use of hybrid and water-in-salt electrolytes, ionic liquids, and non-aqueous electrolytes. Existing aqueous electrolytes are not ideal for industrial-scale production. Suppression of HER and enhanced nitrogen solubility have been observed with hybrid and non-aqueous electrolytes. The engineered electrolytes are very promising though the electrochemical activation has several challenges. The outcome of lithium-mediated nitrogen reduction reaction with engineered non-aqueous electrolyte is highly encouraging.

Ti-doped iron phosphide nanoarrays grown on carbon cloth as a self-supported electrode for enhanced electrocatalytic nitrogen reduction

The electrocatalytic nitrogen reduction reaction (eNRR) has been widely recognized as a promising method for green ammonia synthesis. However, the inert NN bond, inferior catalytic activity and small electrochemically active area impede its practical application. To circumvent these problems, we proposed self-supported Ti-doped iron phosphide (FeP) nanorod arrays grown on carbon cloth (Ti-FeP/CC) as an electrode for eNRR. The introduction of Ti doping sites regulated the electron structure of FeP, leading to electron migration from Fe to P, which facilitated N2-to-NH3 conversion. The as-prepared Ti-FeP/CC showed an enhancement of electrochemical surface area (ECSA), high electrical conductivity and well-exposed active sites. Ti-FeP/CC was capable of producing a high NH3 yield of 10.93 μg h-1 cm-2 and faradaic efficiency of 10.77% at an optimal voltage of -0.3 V (vs. RHE) in a 0.1 M Na2SO4 solution with excellent stability and durability during the eNRR process. This work not only presents a promising electrode material for eNRR, but also provides a new insight into rational heteroatom doping for electrocatalysis.