The electrochemical reduction of N into NH production under ambient conditions represents an attractive prospect for the fixation of N . However, this process suffers from low yield rate of NH over reported electrocatalysts. In this work, a record-high activity for N electrochemical reduction over Ru single atoms distributed on nitrogen-doped carbon (Ru SAs/N-C) is reported. At -0.2 V versus reversible hydrogen electrode, Ru SAs/N-C achieves a Faradaic efficiency of 29.6% for NH production with partial current density of -0.13 mA cm . Notably, the yield rate of Ru SAs/N-C reaches 120.9 μgNH3  mgcat.-1  h-1, which is one order of magnitude higher than the highest value ever reported. This work not only develops a superior electrocatalyst for NH production, but also provides a guideline for the rational design of highly active and robust single-atom catalysts.

Metrics & MoreArticle Recommendations CONSPECTUS: CO 2 is not only a greenhouse gas but also a pivotal carbon source as a promising supplement to fossil fuels. Both the environment and energy crises have compelled the researchers to explore how to efficiently transform CO 2 into liquid fuels and value-added chemicals. As the industrialized approach nowadays, heterogeneous CO 2 hydrogenation driven by thermal energy represents a potential strategy to help mitigate the greenhouse effect and reduce the reliance on fossil fuels. However, as the prerequisite for CO 2 hydrogenation, CO 2 activation is difficult due to the thermodynamic stability and chemical inertness of CO 2 molecules. It is not proper to activate CO 2 by directly increasing the reaction temperature, because CO 2 hydrogenation into liquid products is an exothermic process where elevating the temperature decreases both the balanced conversion of CO 2 and the balanced selectivity for target products. Therefore, the key scientific issue for CO 2 hydrogenation lies in how to design catalysts which enable efficient activation of CO 2 . Up to date, a vast variety of active sites have been constructed for effective activation of CO 2 . These active sites including step sites, alloys, interface, substitution, vacancies, etc. are generally symmetry-breaking rather than perfect flat surfaces. Herein, we propose a catalyst design principle of constructing symmetry-breaking sites to activate nonpolar CO 2 molecules. From the perspective of electronic properties, there is a prominent charge density gradient in a symmetry-breaking center, resulting in perturbing electronic structures of nonpolar CO 2 and polarizing the adsorbed species. From the perspective of adsorption configuration, a symmetry-breaking site gives a local torque which enables more effective overlapping of atomic orbitals and thus more facilely bending of linear CO 2 molecules, compared with symmetric sites. In this Account, we categorize the modes of CO 2 activation and put forward the design principle of constructing symmetry-breaking sites. Moreover, we illustrate how to construct symmetry-breaking sites from the perspectives of local and global structures. Strategies to break the symmetry of local structures include surface substitution, surface adatom, and surface vacancy. Strategies to break the symmetry of global structures comprise surface modification with ligands, high-index surface, and phase reconstruction. In the future, further improvements, such as quantified descriptors, function for C−C coupling, and applicability to other nonpolar molecules, are necessary.

Ru single atoms are distributed on nitrogen‐doped carbon (Ru SAs/N–C), synthesized for efficient electrochemical reduction of N2 by Rui Si, Jie Zeng, and co‐workers, as described in article number https://doi.org/10.1002/adma.201803498. Ru SAs/N–C exhibits a record‐high activity for N2 electrochemical reduction. At −0.2 V vs reversible hydrogen electrode, Ru SAs/N–C achieves a Faradaic efficiency of 29.6% for NH3 production with a yield rate of 120.9 μnormalgNHnormal3  mgcat.−1  normalh−1, which is one order of magnitude higher than the highest value previously reported.