RESUMEN
Oxygen-vacancy (Ov) engineering is an effective strategy to manipulate the electronic configuration of catalysts for electrochemical nitrogen reduction reaction (eNRR). The influence of the stable facet on the electronic configuration of Ov is widely studied, however, the effect of the reactive facet on the local electron density of Ov is unveiled. In this work, an eNRR electrode R(111)-TiO2/HGO is provided with a high proportion exposed reactive facet (111) of rutile-TiO2 (denoted as R(111)-TiO2) nanocrystals with Ov anchored in hierarchically porous graphite oxide (HGO) nanofilms. The R(111)-TiO2/HGO exhibits excellent eNRR performance with an NH3 yield rate of 20.68 µg h-1 cm-2, which is ≈20 times the control electrode with the most stable facet (110) exposed (R(110)-TiO2/HGO). The experimental data and theoretical simulations reveal that the crystal facet (111) has a positive effect on regulating the local electron density around the oxygen vacancy and the two adjacent Ti-sites, promoting the π-back-donation, minimizing the eNRR barrier, and transforming the rate determination step to *NNHâ*NNHH. This work illuminates the effect of crystal facet on the performance of eNRR, and offers a novel strategy to design efficient eNRR catalysts.
RESUMEN
Conventional ammonia production consumes significant energy and causes enormous carbon dioxide (CO2) emissions globally. To lower energy consumption and mitigate CO2 emissions, a facile, environmentally friendly, and cost-effective one-pot method for the synthesis of a ruthenium-based nitrogen reduction nanocatalyst has been developed using reduced graphene oxide (rGO) as a matrix. The nanocatalyst synthesis was based on a single-step simultaneous reduction of RuCl3 into ruthenium-based nanoparticles (Ru-based NPs) and graphene oxide (GO) into rGO using glucose as the reducing agent and stabilizer. The obtained ruthenium-based nanocatalyst with rGO as a matrix (Runano-based/rGO) has shown much higher catalytic activity at lower temperatures and pressures for ammonia synthesis than conventional iron catalysts. The rGO worked as a promising promoter for the electrochemical synthesis of ammonia due to its excellent electrical and thermal conductivity. The developed Runano-based/rGO nanocatalyst was characterized using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), ultraviolet-visible (UV-vis) absorption spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), inductively coupled plasma mass spectrometry (ICP-MS), and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the size of the Ru-based NPs on the surface of rGO was 1.9 ± 0.2 nm and the ruthenium content was 25.03 wt %. Bulk electrolysis measurements were conducted on thin-layer electrodes at various cathodic potentials in a N2-saturated 0.1 M H2SO4 electrolyte at room temperature. From the chronoamperometric measurements, the maximum faradic efficiency (F.E.) of 2.1% for ammonia production on the nanostructured Runano-based/rGO electrocatalyst was achieved at a potential of -0.20 V vs reversible hydrogen electrode (RHE). This electrocatalyst has attained a superior ammonia production rate of 9.14 µg·h-1·mgcat.-1. The results demonstrate the feasibility of reducing N2 into ammonia under ambient conditions and warrant further exploration of the nanostructured Runano-based/rGO for electrochemical ammonia synthesis.