Multitude of complications involved with handling hydrogen fuels has propelled many to consider instead an ammonia economy. Ammonia electrooxidation reaction (AOR) herein is discussed as a means for energy application either by electrochemical decomposition for onsite hydrogen generation or by direct employment of ammonia as a fuel in a direct ammonia fuel cell. The development of a robust and stable AOR catalysts are pivotal for both applications, alongside the development of a high-performing HER and ORR catalysts. Examined here are the different operating conditions for both applications and different hurdles to overcome for the catalyst development. The kinetics and mechanism of ammonia electrooxidation are elucidated to provide a foundation to better understand the issues associated with this technology and a comprehensive review on Pt-free catalysts that have been explored for AOR is presented in order to facilitate future research direction in this promising technology.

Regulating the local environment and structure of metal center coordinated by nitrogen ligands (M‐N4) to accelerate overall reaction dynamics of the electrochemical CO2 reduction reaction (CO2RR) has attracted extensive attention. Herein, we develop an axial traction strategy to optimize the electronic structure of the M‐N4 moiety and construct atomically dispersed nickel sites coordinated with four nitrogen atoms and one axial oxygen atom, which are embedded within the carbon matrix (Ni‐N4‐O/C). The Ni‐N4‐O/C electrocatalyst exhibited excellent CO2RR performance with a maximum CO Faradic efficiency (FE) close to 100 % at −0.9 V. The CO FE could be maintained above 90 % in a wide range of potential window from −0.5 to −1.1 V. The superior CO2RR activity is due to the Ni‐N4‐O active moiety composed of a Ni‐N4 site with an additional oxygen atom that induces an axial traction effect.

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Atomically dispersed and nitrogen-coordinated single Ni sites (i.e., NiNx moieties) embedded in partially graphitized carbon have emerged as effective catalysts for CO2 electroreduction to CO. However, much mystery remains behind...

Ammonia (NH3) has proved to be an effective alternative to hydrogen in low-temperature fuel cells via its direct ammonia oxidation reaction (AOR). However, the kinetically sluggish AOR has prohibitively hindered the attractive direct ammonia fuel cell (DAFC) applications. Here, we report an efficient AOR catalyst, in which ternary PtIrNi alloy nanoparticles well dispersed on a binary composite support consisting of porous silicon dioxide (SiO2) and carboxyl-functionalized carbon nanotube (PtIrNi/SiO2-CNT-COOH) through a sonochemical-assisted synthesis method. The PtIrNi alloy nanoparticles, with the aid of abundant OHad provided by porous SiO2 and the improved electrical conductivity by CNTs, exhibit remarkable catalytic activity for the AOR in alkaline media. It is evidenced by a lower onset potential (∼0.40 V vs reversible hydrogen electrode (RHE)) at room temperature than that of commercial PtIr/C (ca. 0.43 V vs RHE). Increasing NH3 concentrations and operation temperatures can significantly enhance AOR activity of this PtIrNi nanoparticle catalyst. Specifically, the catalyst at the temperature of 80 °C exhibits a much lower onset potential (∼0.32 V vs RHE) and a higher peak current density, indicating that DAFCs operated at a higher temperature are favorable for increased performance. Constant-potential density functional theory (DFT) calculations showed that the Pt–Ir ensembles on {100}-terminated surfaces serve as the active site. The introduction of Ni raises the center energy of the density of states projected onto the group d-orbitals of surface sites and thus lowers the theoretical onset potential for *NH2 dehydrogenation to *NH compared to Pt and Pt3Ir alloy.