Swinging Hydrogen Evolution to Nitrate Reduction Activity in Molybdenum Carbide by Ruthenium Doping

Abstract

A common challenge for electrochemical ammonia synthesis in an aqueous phase is the consumption of Faradaic charge by the competing hydrogen evolution reaction (HER), which reduces the Faradaic efficiency for the desired conversion, i.e., the nitrate reduction reaction (NO 3 RR) to ammonium. This problem is particularly severe when a single-phase catalyst is operated at high current limits, thus a cocatalyst system that works synergistically for hydrogen acquisition and deoxygenation is needed to promote NO 3 RR over HER. Herein, we select a wellknown HER catalyst Mo 2 C and investigate how metal doping can switch its kinetics from HER-dominated to NO 3 RR-dominated pathways. At 3.8 wt % Ru doping of Mo 2 C, a 75% single pass conversion of nitrate (0.1 M) to ammonium in a 16 cm 2 flow electrolyzer was achieved, corresponding to an ammonium yield rate of 9.07 mmol h −1 at a full cell voltage of 2 V. As confirmed by DFT calculations and kinetic isotope experiments, ruthenium dopants in the matrix serve as the sink point for adsorbed hydrogen during NO 3 RR to promote the cooperative deoxygenation of *NO 3 and *NO 2 on the Ru−Mo cocatalytic site. Our study suggests that optimizing hydrogen acquisition and deoxygenation reactions in cocatalytic systems is an effective strategy for electrochemical synthesis.

Single silicon-doped CNT as a metal-free electrode for robust nitric oxide reduction utilizing a Lewis base site: an ingenious electronic “Reflux-Feedback” mechanism

“…Unlike normal nonpolar molecules (N 2 and O 2 ), the asymmetric NO tends to undergo a lateral adsorption conformation (N-side configuration) with the Si atom under the effect of orientation forces, consistent with previous studies. 7,19,30,31 In fact, we also checked the adsorption behavior of the NO molecule before discussing the NORR performance. To be specific, the corresponding comparative data of the diverse adsorption patterns (such as O-end, N-end, and side-on) are added in Table S1 of the ESI.…”

Cu2+1O/Ag Heterostructure for Boosting the Electrocatalytic Nitrate Reduction to Ammonia Performance

“…1−3 Currently, industrial NH 3 production mainly relies on the age-old Haber−Bosch process, which requires relatively harsh reaction conditions including high-temperature (300−550 °C), highpressure (200−350 atm), and Fe-based catalysts, leading to substantial fossil fuel consumption and high CO 2 emissions. 4,5 Therefore, in the context of increasingly exhausted fossil energy and increasingly serious environmental pollution problems, the search for new technologies to replace the Haber−Bosch ammonia production process is urgent and has attracted extensive research interest from scientists. 6−8 Recently, among the various alternative ammonia production methods to the Haber−Bosch process, such as photocatalysis, electrocatalysis, and biocatalysis, the electrocatalytic ammonia production route, with renewable electricity as an energy driver from solar or wind, has been developed in the past few years.…”

“…Ammonia (NH 3 ) is crucial to the development of industry, agriculture, and even the whole mankind due to its wide range of practical applications as the precursor of chemical fertilizers and various chemicals, fuels, and energy carriers. − Currently, industrial NH 3 production mainly relies on the age-old Haber–Bosch process, which requires relatively harsh reaction conditions including high-temperature (300–550 °C), high-pressure (200–350 atm), and Fe-based catalysts, leading to substantial fossil fuel consumption and high CO 2 emissions. , Therefore, in the context of increasingly exhausted fossil energy and increasingly serious environmental pollution problems, the search for new technologies to replace the Haber–Bosch ammonia production process is urgent and has attracted extensive research interest from scientists. − Recently, among the various alternative ammonia production methods to the Haber–Bosch process, such as photocatalysis, electrocatalysis, and biocatalysis, the electrocatalytic ammonia production route, with renewable electricity as an energy driver from solar or wind, has been developed in the past few years. − Electrochemical nitrogen reduction reaction (NRR) is regarded as one of the electrocatalytic ammonia production routes, in which the produced NH 3 comes from the reaction of N 2 and H 2 O in the electrolyte under ambient conditions. − However, due to the strong NN triple bond energy, the extremely low solubility of N 2 in water, and the competing hydrogen evolution reaction (HER), NRR suffers from low activity and selectivity [Faradaic efficiency (FE)]. In addition, the low NH 3 yield rate is often troubled and suspected by environmental NH 3 contamination .…”

Using ternary steric hindrance synergy of a defective MoS2 monolayer to manipulate the electrocatalytic mechanism toward nitric oxide reduction: a first-principles and machine learning study

“…The exploitation of nitric oxide, a byproduct in the combustion of hydrocarbon fuels, has always been a challenge for researchers. 1,2 In addition, its unsafe disposal causes much harm to the ecological environment. At present, nitric oxide can oen be found in soil, lakes, and air dust in the form of stable acid ionic salts, which are harmful for human health and to the environment (nitric oxide is a carcinogen, causes acid rain corrosion and ozone depletion, etc.).…”

“…Even more striking is that via ve pairs of proton-electron pair couples (*NO + 5H + + 5e − / *NH 3 + H 2 O), the target product can theoretically be converted directly into ammonia (NH 3 ) instead of N 2 or N 2 O, a feature with great industrial value. To this end, a great deal of theoretical and experimental studies 1,[9][10][11][12][13] have been devoted to the search for efficient catalysts, but progress has been limited. Mavrikakis et al explored the catalytic performance of the bulk Pt(111) noble metal in the NORR under high NO coverage.…”