Search

Electrochemical carbon dioxide reduction reaction (ECO2RR) is an effective means to promote carbon cycling. Recently, Bi-based metal–organic frameworks (MOFs) have attracted significant attention due to their high efficiency for formic acid generation in ECO2RR, however, their composition and morphology transformation during electrocatalysis still lack a deep exploration. Herein, a Bi-MOF with 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine (H3TATB) ligand is used as the prototype to investigate its in situ transformation during ECO2RR. With various characterization methods, the detailed transformation processes are revealed. Firstly, the Bi-MOF was transformed into Bi2O2CO3 due to ligand substitution in KHCO3 electrolyte, resulting in changes in both shape and composition. Secondly, during ECO2RR, the Bi3+ ions can be reduced into metallic Bi0 nanoparticles and act as the real active component for ECO2RR. The resultant catalyst exhibits a high selectivity of up to 94.3% towards formate generation. At an optimal potential of −1.08 V vs. RHE, the catalyst can maintain a current density of −25 mA cm−2 and a faradaic efficiency of formate over 90% for 14.5 hours. This work not only develops an efficient electrocatalyst for ECO2RR but also provides a new insight into the in situ reconstruction of MOF precursor into the active catalyst, which is useful for the design and synthesis of other materials. [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]

The preparation of Bi nanoclusters confined in porous carbon (Bi NCs@PC) efficiently converts CO 2 to formic acid. In addition, Bi nanoclusters have excellent stability due to the protection of micropores. [Display omitted] • Excellent stability maintaining zero valences of Bi for long-term storage. • High Faradaic efficiency of formic acid above 90 % in a wide voltage range of 500 mV. • In-situ Raman and DFT calculations revealed the reaction intermediates and mechanisms. Electrochemical reduction of CO 2 to formate via renewable electricity is a cost-effective route. However, the existing bismuth-based electrocatalysts are in oxide form and involve in-situ reduction to metallic bismuth during CO 2 reduction. In this work, we demonstrate a nanocomposite electrocatalyst by confining Bi nanoclusters into porous carbons (Bi NCs@PC). In particular, the Bi NCs show excellent stability that can maintain zero valences during long-term electrocatalysis or after months of storage in the air. The as-synthesized Bi NCs@PC catalyst achieves up to 96 % formate Faradaic efficiency (FE) at −1.15 V versus reversible hydrogen electrode. Notably, the FE only attenuates by 7.3 % after 30 days of storage under ambient conditions. In-situ Raman spectrum identify the key intermediates during formate formation. Moreover, Bi NCs encapsulated in carbon micropores could significantly reduce the formation energy of the intermediate *OCHO by density functional theory. [ABSTRACT FROM AUTHOR]

The electrosynthesis of ethanol by CO 2 reduction is mostly achieved on metallic copper electrocatalysts, but confronts low Faradic efficiency (FE) and selectivity. Herein, we report novel electrocatalysts in which Ni nanoparticles are encapsulated in N-rich carbon nanotubes (Ni@NCNT) by chemical vapor deposition method. The optimized Ni@NCNT-700 exhibits a high ethanol FE of 38.5% at −0.5 V and remains over 30% in a wide potential range of −0.5 ∼ −1.2 V. Notably, ethanol is the only liquid product and the total FE for CO and ethanol keeps above 90% in a potential range of −0.6 ∼ −1.2 V vs. reversible hydrogen electrode. A high current density of 128 mA cm−2 is obtained in a 1 M KOH electrolyte at −2.0 V in a flow-cell device. Moreover, In-situ Raman and density functional theory calculations demonstrate that the confinement and synergistic effects of Ni NPs and NCNTs sufficiently lower the energy barrier for C–C coupling and suppressed the *CO desorption. [Display omitted] • Non-Cu based electrocatalysts for ethanol production. • High ethanol FE of 38.5% at low overpotential of −0.5 V vs. RHE as the only liquid product. • Total FE for reduced production (CO and ethanol) over 90% in a wide voltage range of −0.7 ∼ −1.1 V vs. RHE. • Confinement and synergistic effect of N species on NCNTs and Ni NPs reduce the Gibbs free energy barrier for C–C coupling. [ABSTRACT FROM AUTHOR]

[Display omitted] • The electronic properties are modulated to enhance the CO 2 RR activity by triple-heteroatoms doping. • Reaction intermediates are directly detected and analyzed by in-situ Raman spectra. • High CO FE is achieved at a low onset overpotential of 270 mV. • A high current density of 245 mA cm−2 and stable FE CO above 98% are simultaneously achieved in a flow-cell. Electroreduction of CO 2 to value-added chemicals using metal-free carbon catalysts is attractive, but single N-doped carbons suffer from poor efficiency (<90%) and low current density (<2 mA cm−2). Herein, we report a facile and scalable preparation of ternary heteroatoms (N, S, P)-doped carbon electrocatalyst to enhance electrochemical activity, because the multi-heteroatoms with different sizes and electronegativities can modulate the electronic properties to facilitate CO 2 localization and provide abundant active sites with enhanced charge-carrier concentrations. It exhibits high activity toward CO 2 electroreduction to CO activity with 92% CO Faradaic efficiency (FE CO) at −0.7 V RHE and low onset overpotential of 270 mV. The promising potential of industrial application is manifested by the high current density of 245 mA cm−2 and stable FE CO above 98% in a flow-cell configuration. Moreover, in-situ Raman spectroscopy demonstrates that *COOH is the key intermediate in CO 2 -to-CO conversion. Density functional theory calculations reveal that the synergistic effect of N, S, and P heteroatoms boosts the catalytic activity by greatly decreasing the free energy barrier of *COOH formation. Furthermore, the morphological benefit of hierarchically porous structures plays a synergistic role in improving the CO 2 reduction activity. [ABSTRACT FROM AUTHOR]