No abstract

First principles calculations show that gold atoms with low generalized coordination numbers possess high activity for electroreduction of CO2 to CO. Atom-resolved three-dimensional reconstruction reveals that dealloyed nanoporous gold possesses such a favourable structure characteristic, which results in a faradaic efficiency as high as 94% for CO production.

Exploration of efficient catalysts is a priority for the electrochemical nitrogen reduction reaction (NRR) under ambient temperature and pressure. Recently, several nanostructured gold (Au) catalysts have shown impressive catalytic activities toward NRR. However, the atomic origin of high catalytic activities of Au catalysts is vague. In this work, a quantitative relationship between the generalized coordination number (GCN) and NRR activity is established. In particular, the NRR activity is linearly increased with the decrease of GCN values of Au surface atoms. As a proof-of-concept experiment, the NRR activity of nanoporous gold (NPG) with a high proportion of low-coordinated surface atoms is investigated and compared with that of Au octahedra (OCTA) enclosed with (111) facets. As expected, NPG exhibits a high NH 3 production rate of 30.5 μg h −1 mg −1 , which is 5.8 times larger than that of Au OCTA. In addition, the excellent catalytic performance of NPG can be retained for 21 h by showing constant current density, NH 3 production rate, and faradaic efficiency. The findings in this work would provide guiding principles for designing efficient NRR catalysts.

Nanostructured metal catalysts have attracted great interest due to their extraordinary performance for electrocatalysis including electrochemical nitrogen reduction (ENRR). However, their working mechanisms for ENRR are still not fully understood. Herein, seven mono-faceted polyhedral Au nanocrystal were synthesized and systemically compared to elucidate the relation between Au crystal facets and NRR performance. It is found that polyhedra with high-index facets catalytically outperform those with low-index facets. Specifically, Au nanostars (NSs) enclosed with (321) facets show a high NH3 production rate of 2.6 µg h -1 cm -2 (20 µg h -1 mg -2 ) and faradaic efficiency of 10.2% at -0.2 V, which are 3.1 and 5.1 folds larger than nanocubes (NCs) enclosed with (100) facets. As revealed by the theoretical investigation, a larger energy barrier for reduction of H + to H* (∆GH*) hinders occurrence of HER on Au(321) surface, thus ensuring better NRR selectivity. Meanwhile, a lower energy barrier for formation of N2H2* on the catalyst surface and a larger energy barrier for decomposing the formed N2H2* back into N2 and 2H* jointly favor a higher NH3 production rate. This study provides mechanistic insights for ENRR and rational design of metal nanocrystals for electrocatalysis.