Theoretical studies have demonstrated that metal atomic clusters are highly efficient in catalytic ammonia synthesis under mild conditions. However, activation of N2 over atomic clusters from an experimental viewpoint has not been systematically investigated. Here, for the first time, cobalt atomic dimers on a nitrogen–carbon support were synthesized for NH3 synthesis. It is disclosed that N2 activation over Co2 atomic clusters (Co2 ACCs) is entirely different from that over Co single-atom catalysts (Co SACs) or Co nanoparticles (Co NPs). A suite of in situ spectroscopy studies reveal that Co2 ACCs not only provide active sites to promote strong metal–support interactions but also initiate strong interclustering interactions, resulting in electron transfers from Co d-orbitals to antibonding orbitals of N2 molecules. As such, the activation energy of the Co2 ACC catalyst in NH3 synthesis is small. Consequently, the catalytic activity of the developed Ba-promoted Co2 ACC catalyst reached 19.42 mmolNH3 gcat–1 h–1 at 400 °C and 1 MPa, which is much superior than that of other Co-based catalysts under such mild conditions. More importantly, the synthesis strategy of Co2 ACCs has general applicability as demonstrated in the preparation of Fe2 and Mn2 atomic clusters.
Xinyu Wang,Sichen Huo,Yanjie Chen,Mingyi Wang,Ying Dai,Jinlong Zou
Cobalt atom cluster (Co AC )-based electrocatalysts usually exhibit high activity for oxygen reduction reaction (ORR), but display limited performance in oxygen evolution reaction (OER). To enhance their bifunctional catalytic efficiency, it is crucial to tailor the d -orbital electronic structure of Co AC through orbital coupling effect, optimizing the chemisorption of O-intermediates. Herein, a 3 d -4 d orbital coupling strategy is used to construct a Co AC -molybdenum carbide/nanocarbon cake (Co AC -Mo x C/CC) catalyst with a hollow structure for ORR/OER in zinc-air batteries (ZABs). Experimental and theoretical results confirm that the 4 d transition metal Mo, with fewer d electrons and more unfilled orbitals, interacts strongly with Co sites through d - d coupling, promoting electron enrichment and triggering 3 d -orbital electron delocalization. This process accelerates the rate-limiting steps of *OH desorption for ORR and *OOH formation for OER, leading to an ultra-low potential gap of 0.604 V and improved stability. Notably, the Co AC -Mo x C/CC-based liquid and flexible all-solid-state ZABs exhibit excellent performance with high open-circuit voltages of 1.49 and 1.47 V, and power densities of 146.4 and 103.4 mW cm −2 , respectively, highlighting their potential to replace precious metal catalysts. This study may open new avenues for manipulating the electronic properties of Co AC -based electrocatalysts and boosting activity through the d - d orbital coupling strategy.
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