The industrial Haber-Bosch process to produce ammonia (NH3) from dinitrogen (N2) is crucial for modern society. However, N2 activation is inherently challenging and the Haber-Bosch process has significant drawbacks, as it is highly energy intensive, not sustainable due to substantial CO2 emissions primarily from the generation of H2 and requires large-centralized facilities. New strategies of sustainable N2 activation, such as low-temperature thermochemical catalysis and (photo)electrocatalysis, have been pursued, but progress has been hindered by the lack of rigor and reproducibility in the collection and analysis of results.In this Primer, we provide a holistic step-by-step protocol, applicable to all nitrogen-transformation reactions, focused on verifying genuine N2 activation by accounting for all contamination sources. We compare state-of-the-art results from different catalytic reactions following the protocol's framework, and discuss necessary reporting metrics and ways to interpret both experimental and density functional theory results. This Primer covers various common pitfalls in the field, best practices to improve reproducibility and cost-efficient methods to carry out rigorous experimentation. The future of nitrogen catalysis will require an increase in rigorous experimentation and standardization to prevent false positives from appearing in the literature, which can enable advancing towards practical technologies for the activation of N2.

Summary Green synthesis of ammonia by electrochemical nitrogen reduction reaction (NRR) shows great potential as an alternative to the Haber-Bosch process but is hampered by sluggish production rate and low Faradaic efficiency. Recently, lithium-mediated electrochemical NRR has received renewed attention due to its reproducibility. However, further improvement of the system is restricted by limited recognition of its mechanism. Herein, we demonstrate that lithium-mediated NRR began with electrochemical deposition of lithium, followed by two chemical processes of dinitrogen splitting and protonation to ammonia. Furthermore, we quantified the extent to which the freshly deposited active lithium lost its activity toward NRR due to a parasitic reaction between lithium and electrolyte. A high ammonia yield of 0.410 ± 0.038 μg s −1 cm −2 geo and Faradaic efficiency of 39.5 ± 1.7% were achieved at 20 mA cm −2 geo and 10 mA cm −2 geo, respectively, which can be attributed to fresher lithium obtained at high current density.

Ammonia synthesis by electrochemical nitrogen reduction reaction (NRR) is a promising alternative to the Haber−Bosch process. Accurate measurement of produced ammonia requires rigorous criteria, which rely on a deeper understanding of ammonia characteristics. Herein, we systematically investigated the interaction of ammonia with Nafion membrane and electrolyte to reveal factors that may induce deviation in ammonia measurements. We demonstrated desirable characteristics of Nafion membrane as a separator in view of the low adsorption rate and low diffusion rate for ammonia. But one should be aware of the possible contaminants pre-existing in the membrane. It was also observed that the acid electrolyte had a much greater affinity for ammonia compared with base electrolyte. Specifically, the acid electrolyte is more vulnerable to potential ammonia contaminant in the feeding gas, whereas base electrolyte is inclined to lose produced ammonia under a continuous nitrogen flow. The findings provide a deeper understanding of ammonia's behavior in NRR test and help obtain accurate and credible ammonia measurements.

The crucial role of electrolyte cations in CO2 electroreduction has received intensive attention. One prevailing theory is that through electrostatic interactions or direct coordination, larger cations such as Cs+ can better stabilize the key intermediate species for CO and multicarbon (C2+) product generation, for example, on silver and copper. Herein, we show that smaller, acidic alkali metal cations greatly enhance CO2-to-methanol conversion kinetics (Li+ > Na+ > K+ > Cs+) on an immobilized molecular cobalt catalyst unlike the trend for CO and C2+. Through kinetic isotope effect studies and electrokinetic analyses, we found that hydration shell of a cation serves as a proton donor in the rate-determining protonation step of adsorbed CHO where acidic cations promote the proton-coupled electron transfer. This study reveals the promotional effect of cation solvation environment on CO2 electroreduction beyond the widely acknowledged stabilizing effect of cations.

Nitrogen is essential for plant growth, and specifically activated nitrogen in the form of ammonia is used as a synthetic fertilizer (~80%), thereby providing sustenance for roughly half of the global population. The century-old industrial Haber-Bosch process for the production of ammonia is therefore crucial for modern society, but the process unfortunately has significant drawbacks. Nitrogen is extremely inert, and the process is highly energy intensive, not sustainable due to substantial CO2 emissions, and requires large-centralized facilities due to the inherent challenge of activating N2 via high temperatures and pressures. New strategies which would enable sustainable and decentralized production for N2 fixation, such as low-temperature thermochemical catalysis, electrocatalysis, and photo(electro)catalysis, have been pursued over the past few decades. Unfortunately, efforts particularly in electron and photon-assisted N2 fixation have been filled with controversies and contradictory results, while progress has been hindered by the lack of rigor and reproducibility in the collection and analysis of results. This is due to ammonia and other N-containing contaminants being ubiquitous in the environment, which can easily lead to contamination, inflation of reported catalytic performance, and thereby reporting of false positives.In this work, we provide a holistic step-by-step protocol, applicable to all nitrogen-transformation reactions, focused on verifying genuine N2 activation by accounting for all possible contamination sources. The possible sources of contamination, denoted as the system mass, include aspects such as flow gas impurities, impurities in the catalyst/substrate, electrolyte contaminants (for electrolytic systems), and impurities in the absorber material (for photocatalytic systems), among other sources. If the amount of product measured is less than the system mass, scientists need to include quantifiable isotope labelled experimentation coupled with proper gas cleaning to elucidate the source of the activated nitrogen. We focus primarily on electrochemical, photo(electro)chemical, and thermochemical systems due to the size of interest in the fields, but the protocol finds wider applicability to other modes of N2 activation, such as plasma and mechanochemical N2 fixation. Using the protocol’s framework, state-of-the-art results from different catalytic reactions are quantitatively assessed which reveal a number of important insights: 1) to explain why obtaining reliable results for electrochemical and photo(electro)chemical systems are inherently more challenging than thermochemical systems, leaving quantitative isotope experiments as the only cost-effective ways to verify genuine N2 activation. 2) to flag the potential problems related to low-temperature (<250 oC) thermochemical catalysis results due to the alarmingly low product formed in relation to their system size from which contaminants may emerge. 3) to provide an updated and realistic picture of the N2 activation fields in the cont...

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