RESUMEN
By utilizing a supramolecular complex rather than an individual molecule as a deformable and elastic substitutional component, we put forward a solid-solution strategy and demonstrate an example of how two related yet non-isostructural crystalline host-guest compounds can form molecular solid solutions. Interestingly, such a strategy can effectively and continuously modulate the molecular motion and phase transition in them, as revealed by the variable-temperature/frequency dielectric responses.
RESUMEN
Developing the low-cost and efficient single-atom catalysts (SACs) for nitrogen reduction reaction (NRR) is of great importance while remains as a great challenge. The catalytic activity, selectivity and durability are all fundamentally related to the elaborate coordination environment of SACs. Using first-principles calculations, we investigated the SACs with single transition metal (TM) atom supported on defective boron carbide nitride nanotubes (BCNTs) as NRR electrocatalysts. Our results suggest that boron-vacancy defects on BCNTs can strongly immobilize TM atoms with large enough binding energy and high thermal/structural stability. Importantly, the synergistic effect of boron nitride (BN) and carbon domains comes up with the modifications of the charge polarization of single-TM-atom active site and the electronic properties of material, which has been proven to be the essential key to promote N2 adsorption, activation, and reduction. Specifically, six SACs (namely V, Mn, Fe, Mo, Ru, and W atoms embedded into defective BCNTs) can be used as promising candidates for NRR electrocatalysts as their NRR activity is higher than the state-of-the art Ru(0001) catalyst. In particular, single Mo atom supported on defective BCNTs with large tube diameter possesses the highest NRR activity while suppressing the competitive hydrogen evolution reaction, with a low limiting potential of -0.62â V via associative distal path. This work suggests new opportunities for driving NH3 production by carbon-based single-atom electrocatalysts under ambient conditions.
RESUMEN
The production of ammonia (NH3) from molecular dinitrogen (N2) under ambient conditions is of great significance but remains as a great challenge. Using first-principles calculations, we have investigated the potential of using a transition metal (TM) atom embedded on defective MXene nanosheets (Ti3-xC2Oy and Ti2-xCOy with a Ti vacancy) as a single-atom electrocatalyst (SAC) for the nitrogen reduction reaction (NRR). The Ti3-xC2Oy nanosheet with Mo and W embedded, and the Ti2-xC2Oy nanosheet with Cr, Mo, and W embedded, can significantly promote the NRR while suppressing the competitive hydrogen evolution reaction, with the low limiting potential of -0.11 V for W/Ti2-xC2Oy. The outstanding performance is attributed to the synergistic effect of the exposed Ti atom and the TM atom around an extra oxygen vacancy. The polarization charges of the active center are reasonably tuned by the embedded TM atoms, which can optimize the binding strength of key intermediate *N2H. The good feasibility of preparing such TM SACs on defective MXenes and the high NRR selectivity with regard to the competitive HER suggest new opportunities for driving NH3 production by MXene-based SAC electrocatalysts under ambient conditions.
RESUMEN
Developing metal-free catalysts for reduction of CO2 into energy-rich products is a popular yet very challenging topic. Using density functional theory calculations, we investigated the electrocatalytic performance of C-doped and line-defect (Ld)-embedded boron nitride nanoribbons (BNNRs) for CO2 reduction reaction (CRR). Because of the presence of bare edge B atoms neighboring to C dopant and C2 dimer as active sites, defective BNNRs exhibit high CRR catalytic activity and selectivity. The Ld-embedded BNNR structures with C2 dimer can not only convert CO2 into CO with very low overpotential of -0.5 V versus reversible hydrogen electrode but also ensure high selectivity in deactivating the hydrogenation channel of the desorbed CO to CH4. The C-doped zigzag and armchair BNNRs bind strongly to the CO intermediate and thus promote the selective conversion of CO2 to CH4, with the lower energy cost on the armchair ribbon than the zigzag one. The presence of edge B atoms and C dopant as dual active sites in BNNRs enables effective couplings between *CH2 and CO intermediates, leading to the formation of C2 products including C2H4 and C2H5OH, with a high selectivity for C2H5OH. Importantly, unwanted hydrogen evolution reaction is suppressed during CRR catalyzed by these BNNR-based configurations. Overall, the present findings highlight a promising new class of low-cost, metal-free electrocatalysts combining high CRR activity and selectivity.