RESUMO
Electrochemical formic acid oxidation reaction (FAOR) is a pivotal model for understanding organic fuel oxidation and advancing sustainable energy technologies. Here, we present mechanistic insights into a novel molecular-like iridium catalyst (Ir-N4-C) for FAOR. Our studies reveal that isolated sites facilitate a preferential dehydrogenation pathway, circumventing catalyst poisoning and exhibiting high inherent activity. In-situ spectroscopic analyses elucidate that weakly adsorbed intermediates mediate the FAOR and are dynamically regulated by potential-dependent redox transitions. Theoretical and experimental investigations demonstrate a parallel mechanism involving two key intermediates with distinct pH and potential sensitivities. The rate-determining step is identified as the adsorption of formate via coupled or sequential proton-electron transfer, which aligns well with the observed kinetic properties, pH dependence, and hydrogen/deuterium isotope effects in experiments. These findings provide valuable insights into the reaction mechanism of FAOR, advancing our understanding at the molecular level and potentially guiding the design of efficient catalysts for fuel cells and electrolyzers.
RESUMO
Electrocatalytic nitrate reduction reaction (NO3-RR) is an important route for sustainable NH3 synthesis and environmental remediation. Metal-organic frameworks (MOFs) are one family of promising NO3-RR electrocatalysts, however, there is plenty of room to improve in their performance, calling for new design principles. Herein, a MOF-on-MOF heterostructured electrocatalyst with interfacial dual active sites and build-in electric field is fabricated for efficient NO3-RR to NH3 production. By growing Co-HHTP (HHTP=2,3,6,7,10,11-hexahydroxytriphenylene) nanorods on Ni-BDC (BDC=1,4-benzenedicarboxylate) nanosheets, experimental and theoretical investigations demonstrate the formation of Ni-O-Co bonds at the interface of MOF-on-MOF heterostructure, leading to dual active sites tailed for NO3-RR. The Ni sites facilitate the adsorption and activation of NO3-, while the Co sites boost the H2O decomposition to supply active hydrogen (Hads) for N-containing intermediates hydrogenation on adjacent Ni sites, cooperatively reducing the energy barriers of NO3-RR process. Together with the accelerated electron transfer enabled by built-in electric field, remarkable NO3-RR performance is achieved with an NH3 yield rate of 11.46 mg h-1 cm-2 and a Faradaic efficiency of 98.4%, outperforming most reported MOF-based electrocatalysts. This work provides new insights into the design of high-performance NO3-RR electrocatalysts.
RESUMO
As one of the potential catalysts, disordered solid solution alloys can offer a wealth of catalytic sites. However, accurately evaluating their activity localization structure and overall activity from each individual site remains a formidable challenge. Herein, an approach based on density functional theory and machine learning was used to obtain a large number of sites of the Pt-Ru alloy as the model multisite catalyst for the hydrogen evolution reaction. Subsequently, a series of statistical approaches were employed to unveil the relationship between the geometric structure and overall activity. Based on the radial frequency distribution of metal elements and the distribution of ΔGH, we have identified the surface and subsurface sites occupied by Pt and Ru, respectively, as the most active sites. Particularly, the concept of equivalent site ratio predicts that the overall activity is highest when the Ru content is 20-30%. Furthermore, a series of Pt-Ru alloys were synthesized to validate the proposed theory. This provides crucial insights into understanding the origin of catalytic activity in alloys and thus will better guide the rational development of targeted multisite catalysts.
