Unexpectedly high stability and surface reconstruction of PdAuAg nanoparticles for formate oxidation electrocatalysis

Surface Reconstruction of Single-Twinned AgPdIr Nanoalloy during the Formate Oxidation and Dehydrogenation Reactions

Formate has emerged as a promising energy carrier to generate electrons via formate oxidation reaction (FOR) and hydrogen via formate dehydrogenation reaction (FDR), and it is desirable but difficult to design a novel bifunctional (electro)catalyst to improve reaction kinetics. Herein, we construct the single-twinned AgPdIr (t-AgPdIr) nanoalloy to improve the catalytic activity and stability for the formate oxidation and dehydrogenation processes. The t-AgPdIr nanoalloy, characterized by a distinctive twinned structure with strains and a downshift of the d-band center, demonstrates an improved peak current density of 4.6 A·mgPd -1, a diminished onset potential of 0.45 V, a superior activity retention of 55.7% after 600 cycles, and a current density of 0.73 A·mgPd -1 following potentiostatic polarization for 3600 s. Additionally, the t-AgPdIr catalyst shows an enhanced turnover frequency value of 407.3 h-1, a higher volume of generated H2 gas up to 51.8 mL after 120 min of reaction, and an activity recovery of 90.7% after five reaction cycles. Impressively, compared with the as-prepared nanoalloy, the postreaction catalyst shows a stable strain state along the twin boundaries and a surface segregation of Pd and Ir elements after the formate oxidation and dehydrogenation reactions.

Electrochemical Redox Conversion of Formate to CO via Coupling Fe-Co Layered Double Hydroxides and Au Catalysts

Formate has been considered an inactive molecule and thus cannot be further reduced under CO2 reduction conditions, which limits its widespread application as feedstock. Here we present an electrochemical redox conversion of formate to CO through the potential-dependent generation of carbon dioxide radical anions (CO2 ⋅- ) on Fe-Co layered double hydroxides (Fe-Co LDHs) and the subsequent reduction of CO2 ⋅- to CO on Au catalysts. We present an electrodeposition protocol for the synthesis of Fe-Co LDHs with precise composition control and find that Fe1 Co4 exhibits a promising potential window for CO2 ⋅- formation between 1.14 and 1.4 V and an optimized potential at 1.24 V at a neutral pH condition. We further determined the formation of CO2 ⋅- at 1.24 V via electron paramagnetic resonance and CO2 at >1.4 V through differential electrochemical mass spectrometry. This work provides a redox chemistry route for converting formate into CO through a coupled slit parallel-plate electrode system.

Silver nanomaterials: synthesis and (electro/photo) catalytic applications

In view of their unique characteristics and properties, silver nanomaterials (Ag NMs) have been used not only in the field of nanomedicine but also for diverse advanced catalytic technologies. In this comprehensive review, light is shed on general synthetic approaches encompassing chemical reduction, sonochemical, microwave, and thermal treatment among the preparative methods for the syntheses of Ag-based NMs and their catalytic applications. Additionally, some of the latest innovative approaches such as continuous flow integrated with MW and other benign approaches have been emphasized that ultimately pave the way for sustainability. Moreover, the potential applications of emerging Ag NMs, including sub nanomaterials and single atoms, in the field of liquid-phase catalysis, photocatalysis, and electrocatalysis as well as a positive role of Ag NMs in catalytic reactions are meticulously summarized. The scientific interest in the synthesis and applications of Ag NMs lies in the integrated benefits of their catalytic activity, selectivity, stability, and recovery. Therefore, the rise and journey of Ag NM-based catalysts will inspire a new generation of chemists to tailor and design robust catalysts that can effectively tackle major environmental challenges and help to replace noble metals in advanced catalytic applications. This overview concludes by providing future perspectives on the research into Ag NMs in the arena of electrocatalysis and photocatalysis.

Synthesis and Characterization of PdAgNi/C Trimetallic Nanoparticles for Ethanol Electrooxidation

The direct use of ethanol in fuel cells presents unprecedented economic, technical, and environmental opportunities in energy conversion. However, complex challenges need to be resolved. For instance, ethanol oxidation reaction (EOR) requires breaking the rigid C–C bond and results in the generation of poisoning carbonaceous species. Therefore, new designs of the catalyst electrode are necessary. In this work, two trimetallic Pd_xAg_yNi_z/C samples are prepared using a facile borohydride reduction route. The catalysts are characterized by X-ray diffraction (XRD), Energy-Dispersive X-ray spectroscopy (EDX), X-ray photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM) and evaluated for EOR through cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The XRD patterns have shown a weak alloying potential between Pd, and Ag prepared through co-reduction technique. The catalysts prepared have generally shown enhanced performance compared to previously reported ones, suggesting that the applied synthesis may be suitable for catalyst mass production. Moreover, the addition of Ag and Ni has improved the Pd physiochemical properties and electrocatalytic performance towards EOR in addition to reducing cell fabrication costs. In addition to containing less Pd, The PdAgNi/C is the higher performing of the two trimetallic samples presenting a 2.7 A/mg_Pd oxidation current peak. The Pd₄Ag₂Ni₁/C is higher performing in terms of its steady-state current density and electrochemical active surface area.

Deep reinforcement learning for predicting kinetic pathways to surface reconstruction in a ternary alloy

The majority of computational catalyst design focuses on the screening of material components and alloy composition to optimize selectivity and activity for a given reaction. However, predicting the metastability of the alloy catalyst surface at realistic operating conditions requires an extensive sampling of possible surface reconstructions and their associated kinetic pathways. We present CatGym, a deep reinforcement learning (DRL) environment for predicting the thermal surface reconstruction pathways and their associated kinetic barriers in crystalline solids under reaction conditions. The DRL agent iteratively changes the positions of atoms in the near-surface region to generate kinetic pathways to accessible local minima involving changes in the surface compositions. We showcase our agent by predicting the surface reconstruction pathways of a ternary Ni3Pd3Au2(111) alloy catalyst. Our results show that the DRL agent can not only explore more diverse surface compositions than the conventional minima hopping method, but also generate the kinetic surface reconstruction pathways. We further demonstrate that the kinetic pathway to a global minimum energy surface composition and its associated transition state predicted by our agent is in good agreement with the minimum energy path predicted by nudged elastic band calculations.

Bifunctional Palladium Hydride Nanodendrite Electrocatalysts for Hydrogen Evolution Integrated with Formate Oxidation

The rational design of advanced electrocatalysts and energy-saving electrolysis strategies is highly desirable for achieving high-efficiency electrochemical H₂ generation yet challenging. In this work, we report highly branched Pd hydride nanodendrites (PdH-NDs) formed by a very facial solvothermal method and a succedent chemical H intercalation method in N,N-dimethylformamide. The electrocatalytic performance of PdH-NDs is experimentally and theoretically correlated with the morphology and composition, which has demonstrated substantially enhanced electrochemical activity and stability for formate oxidation reaction and hydrogen evolution reaction in alkaline electrolyte compared with Pd nanodendrites. Density functional theory calculations suggest a downshift of the Pd d-band center of PdH-NDs due to the dominant Pd-H ligand effects that weaken the binding energies of the intermediate catalytic species and toxic carbon monoxide. The asymmetric formate electrolyzer based on bifunctional PdH-ND electrocatalysts is first constructed, which only requires a low voltage of 0.54 V at 10 mA cm^-2 for continuous H₂ generation. This study reveals significant insights about the morphology/composition-performance relationship for palladium hydrides with bifunctional electroactivity.