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.

Proton exchange membrane water electrolysis (PEMWE) is a key technology to solve the serious energy and environmental problems. However, the poor durability of electrocatalysts in acidic oxygen evolution reaction (OER) environment hinders the large-scale application of PEMWE. Herein, a robust RuMn electrochemical catalyst with a remarkable durability within 20 000 cyclic voltammetry cycles is reported. Furthermore, RuMn is stable for 720 h at 10 mA cm -2 current density in 0.5 M H 2 SO 4 solution with <100 mV overpotential increase, outperforming the most electrocatalysts reported to date, by far. An amorphous RuO x shell is detected after the OER test, indicating a surface reconstruction process on the catalyst that inhibits steady-state dissolution. Further study demonstrates that the excellent durability of RuMn realized by protective RuO x can be attributed to strong bond strength of Ru, which is supported by density functional theory calculations with high dissolution voltage. Thus, improving the bond strength of Ru extends the design strategy for the Ru-based alloy catalysts with considerable stability.

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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.

Developing efficient oxygen reduction reaction (ORR) electrocatalysts is critical to fuel cells and metal–oxygen batteries, but also greatly hindered by the limited Pt resources and the long-standing linear scaling relationship (LSR). In this study, ∼6 nm and highly uniform Pd nanospheres (NSs) having surface-doped (SD) P–O species are synthesized and evenly anchored onto carbon blacks, which are further simply heat-treated (HT). Under alkaline conditions, Pd/SDP–O NSs/C-HT exhibits respective 8.7 (4.3)- and 5.0 (5.5)-fold enhancements in noble-metal-mass- and area-specific activity (NM-MSA and ASA) compared with the commercial Pd/C (Pt/C). It also possesses an improved electrochemical stability. Besides, its acidic ASA and NM-MSA are 2.9 and 5.1 times those of the commercial Pd/C, respectively, and reach 65.4 and 51.5% of those of the commercial Pt/C. Moreover, it also shows nearly ideal 4-electron ORR pathways under both alkaline and acidic conditions. The detailed experimental and theoretical analyses reveal the following: (1) The electronic effect induced by the P–O species can downshift the surface d-band center to weaken the intermediate adsorptions, thus preserving more surface active sites. (2) More importantly, the potential hydrogen bond between the O atom in the P–O species and the H atom in the hydrogen-containing intermediates can in turn stabilize their adsorptions, thus breaking the ORR LSR toward more efficient ORRs and 4-electron pathways. This study develops a low-cost and high-performance ORR electrocatalyst and proposes a promising strategy for breaking the ORR LSR, which may be further applied in other electrocatalysis.

A feasible membrane electrode assembly (MEA) configuration is proposed for lithium-mediated electrochemical nitrogen reduction to ammonia, which shows the advantages of efficient gas transfer, reduced solvent consumption and compact configuration.

Electrochemical nitrogen reduction reaction (NRR) is intensively investigated by researchers for its potential to be the nextgeneration technology to produce ammonia. Many attempts have been made to explore the possibility of electrochemical ammonia production catalyzed by noble metals. However, the produced ammonia in most reported cases is in ppm level or even lower, which is susceptible to potential contaminants in experiments, leading to fluctuating or even contradictory results. Herein, a rigorous procedure was adopted to systemati-cally evaluated the performance of commercial noble metal nanocatalysts toward NRR. No discernible amount of ammonia was detected in either acidic or alkaline solutions. Further, nitrogen-containing contaminants in catalysts that might cause false positive results were detected and characterized. An effective way to remove pre-existing pollutants by consecutive cyclic voltammetry scan was proposed, helping to obtain reliable and reproducible results.