Subnanometric metal clusters usually have unique electronic structures and may display electrocatalytic performance distinctive from single atoms (SAs) and larger nanoparticles (NPs). However, the electrocatalytic performance of clusters, especially the size-activity relationship at the sub-nanoscale, is largely unexplored. Here, we synthesize a series of Ru nanocrystals from single atoms, subnanometric clusters to larger nanoparticles, aiming at investigating the size-dependent activity of hydrogen evolution in alkaline media. It is found that the d band center of Ru downshifts in a nearly linear relationship with the increase of diameter, and the subnanometric Ru clusters with d band center closer to Femi level display a stronger water dissociation ability and thus superior hydrogen evolution activity than SAs and larger nanoparticles. Benefiting from the high metal utilization and strong water dissociation ability, the Ru clusters manifest an ultrahigh turnover frequency of 43.3 s−1 at the overpotential of 100 mV, 36.1-fold larger than the commercial Pt/C.

The electrochemical nitrate (NO3-) reduction reaction (NO3-RR), with much rapider kinetics than the nitrogen (N2) reduction, provides new opportunities to harvest ammonia (NH3) under ambient conditions. However, the NH3 production...

Electrochemical nitrate (NO 3 -) reduction reaction (NO 3 -RR) represents as an ideal route for the production of ammonia (NH 3 ) under ambient conditions. Although a markedly improved NH 3 production rate has achieved on the NO -RR than the nitrogen reduction reaction (NRR), the NH 3 production rate of NO 3 -RR is still well below the industrial Haber−Bosch route due to the lack of robust electrocatalysts for yielding high current densities with concurrently good suppression of hydrogen evolution reaction (HER). Herein, we develop an in-situ electrochemical strategy for the synthesis of hollow carbon-coated Cu nanoparticles (NPs) with abundant grain boundaries (HSCu-AGB@C) for highly efficient NO 3 -RR in both alkaline and neutral media. Impressively, in alkaline media, the HSCu-AGB@C can achieve a maximum NH 3 Faradic efficiency of 94.2% with an ultrahigh NH 3 rate of 487.8 mmol g -1 cat h -1 at -0.2 V versus a reversible hydrogen electrode, more than 2.4-fold of the rate obtained on the Haber-Bosch. Both theoretic computations and experimental results uncover that the grain boundaries play the key to improve the NO 3 -RR performance. Provided here the industrial-scale NH 3 production rate may open exciting opportunities for the practical electrosynthesis NH 3 under ambient conditions.

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