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3d transition metal catalysts are effective for the electrocatalytic nitrogen (N2) reduction reaction (NRR) to produce ammonia (NH3), but the role of active sites remains elusive. Herein, a series of iron–cobalt oxyhydroxide hollow nanocages (FeCoOOH HNCs) were constructed via controlled Co doping. The as-obtained FeCoOOH HNCs with an Fe/Co ratio of 1 : 1 exhibited a high faradaic efficiency of 14.7% and superior NH3 formation rate of 16.8 µg h−1 mgcat−1 at −0.3 V vs. RHE. In situ Raman spectra disclose the existence of intermediates and identify the reaction pathway. Density functional theory (DFT) calculations reveal that Co doping could lower the energy barrier of *N2 → *NNH → *NNHH, induced by the preferential proton adsorption on Co sites to drive NH3 electrosynthesis. Moreover, FeCoOOH HNCs with a suitable Fe/Co ratio could boost the *N2 activation due to the bolstered polarization of adsorbed N2, while increasing the energy barrier for the hydrogen evolution reaction. This work provides an intriguing strategy towards efficient NRR electrocatalysis by the elaborate design of two 3d transition metals. [ABSTRACT FROM AUTHOR]

Electroreduction of N2 to NH3 at ambient conditions using renewable electricity is promising, but developing efficient electrocatalysts is still challenging due to the inertness of N≡N bonds. Layer double hydroxides (LDHs) composed of first‐row transition metals with empty d‐orbitals are theoretically promising for N2 electroreduction (NRR) but rarely reported. Herein, hollow NiCo‐LDH nanocages with different Ni/Co ratios were prepared, and their electronic structures and atomic arrangements were critical. The synergetic mechanisms of Ni and Co ions were revealed, and the optimized catalytic sites were proposed. Besides, in‐situ Raman spectroscopy and 15N2 isotopic labeling studies were applied to detect reaction intermediates and confirm the origin of NH3. As a result, high NH3 yield of 52.8 μg h−1 mgcat−1 and faradaic efficiency of 11.5 % were obtained at −0.7 V, which are top‐ranking among Co/Ni‐based NRR electrocatalysts. This work elucidates the structure–activity relationship between LDHs and NRR and is instructive for rational design of LDH‐based electrocatalysts. [ABSTRACT FROM AUTHOR]

Facilely tailored electrocatalyst with high-efficiency and durability for carbon dioxide (CO2) to carbon monoxide (CO) conversion is appealing but remains challenging. Herein, small nickel nanoparticles (about 19.4 nm) confined in nitrogen-doped carbon (Ni NPs@N–C) with narrow size distribution are successfully constructed via a facile one-step calcination strategy of Ni containing MOF compounds. By virtue of the protective N-doped graphitized carbon shell and the uniformly distributed fine Ni nanoparticles in a narrow range from 13 to 21 nm, the as-obtained Ni NPs@N–C can exclusively convert CO2 into CO with excellent Faradaic efficiency (FE) of 96.8% at − 1.0 V (vs. RHE), as well as the superior long-term catalytic stability over 24 h. Moreover, a high current density of more than 200 mA cm−2 with a stable CO FE of 92% can be achieved in a flow cell configuration. This work paves a new way for the facile and potentially scale preparation of small metal nanoparticles for efficient CO2- to-CO conversion. [ABSTRACT FROM AUTHOR]