Trimetallic Ru@AuPt core-shell nanostructures: The effect of microstrain on CO adsorption and electrocatalytic activity of formic acid oxidation

Boosted formic acid electro-oxidation on platinum nanoparticles and "mixed-valence" iron and nickel oxides

The modification of Pt nanoparticles (nano-Pt, assembled electrochemically onto a glassy carbon (GC) substrate) with hybrid multivalent nickel (nano-NiO_x) and iron (nano-FeO_x) oxide nanostructures was intended to steer the mechanism of the formic acid electro-oxidation (FAO) in the desirable dehydrogenation pathway. This binary modification with inexpensive oxides succeeded in mediating the reaction mechanism of FAO by boosting reaction kinetics "electron transfer" and amending the surface geometry of the catalyst against poisoning. The sequence of deposition was optimized where the a-FeO_x/NiO_x/Pt/GC catalyst (where "a" denotes a post-activation step for the catalyst at -0.5 V in 0.5 mol L^-1 NaOH) reserved the best hierarchy. Morphologically, while nano-Pt appeared to be spherical (ca. 100 nm in average diameter), nano-NiO_x appeared as flowered nanoaggregates (ca. 56 nm in average diameter) and nano-FeO_x (after activation) retained a plate-like nanostructure (ca. 38 nm in average diameter and 167 nm in average length). This a-FeO_x/NiO_x/Pt/GC catalyst demonstrated a remarkable catalytic efficiency (125 mA mg_Pt^-1) for FAO that was ca. 12.5 times that of the pristine Pt/GC catalyst with up to five times improvement in the catalytic tolerance against poisoning and up to -214 mV shift in the FAO's onset potential. Evidences for equipping the a-FeO_x/NiO_x/Pt/GC catalyst with the least charge transfer resistance and the highest stability among the whole investigated catalysts are provided and discussed.

Coupling homogeneous and heterogeneous catalysis for enhancement of HCOOH electrooxidation via the dehydrogenation pathway

The homogeneous/heterogeneous catalyst combination of VO²⁺ in anolyte with Pd/C at the anode is first introduced in a formic acid fuel cell to enhance HCOOH electrooxidation. The VO²⁺/Pd catalyst combination establishes a stepwise reaction pathway involving HCOOH dehydrogenation to form V³⁺ from VO²⁺ reduction and subsequent V³⁺ electrooxidation to regain VO²⁺. The fuel cell with the VO²⁺/Pd combination presents a peak power density of 341.3 mW cm^-2 and stable power density higher than 30 mW cm^-2.

Hot Carrier Lifetimes and Electrochemical Water Dissociation Enhanced by Nickel Doping of a Plasmonic Electrocatalyst

Hot carriers generated by localized surface plasmon resonance (LSPR) excitation of plasmonic metal nanoparticles are known to enhance electrocatalytic reactions. However, the participation of plasmonically generated carriers in interfacial electrochemical reactions is often limited by fast relaxation of these carriers. Herein, we address this challenge by tuning the electronic structure of a plasmonic electrocatalyst. Specifically, we design an electrocatalyst for alkaline hydrogen evolution reaction (HER) that consists of nanoparticles of a ternary Cu-Pt-Ni ternary alloy. The CuPt alloy has both plasmonic attributes and electrocatalytic HER activity. Ni doping contributes an electron-deficient 3d band and fully filled 4s band, which promotes water adsorption and prolongs the lifetimes of excited carriers generated by plasmonic excitation. As an outcome, the Cu-Pt-Ni nanoparticles exhibit boosted activity for electrochemical water dissociation and HER under LSPR excitation.

Tailor-designed nanowire-structured iron and nickel oxides on platinum catalyst for formic acid electro-oxidation

This investigation is concerned with designing efficient catalysts for direct formic acid fuel cells. A ternary catalyst containing iron (nano-FeOx) and nickel (nano-NiOx) nanowire oxides assembled sequentially onto a bare platinum (bare-Pt) substrate was recommended for the formic acid electro-oxidation reaction (FAOR). While nano-NiOx appeared as fibrillar nanowire bundles (ca. 82 nm and 4.2 μm average diameter and length, respectively), nano-FeOx was deposited as intersecting nanowires (ca. 74 nm and 400 nm average diameter and length, respectively). The electrocatalytic activity of the catalyst toward the FAOR depended on its composition and loading sequence. The FeOx/NiOx/Pt catalyst exhibited ca. 4.8 and 1.6 times increases in the catalytic activity and tolerance against CO poisoning, respectively, during the FAOR, relative to the bare-Pt catalyst. Interestingly, with a simple activation of the FeOx/NiOx/Pt catalyst at −0.5 V vs. Ag/AgCl/KCl (sat.) in 0.2 mol L⁻¹ NaOH, a favorable Fe²⁺/Fe³⁺ transformation succeeded in mitigating the permanent CO poisoning of the Pt-based catalysts. Interestingly, this activated a-FeOx/NiOx/Pt catalyst had an activity 7 times higher than that of bare-Pt with an ca. −122 mV shift in the onset potential of the FAOR. The presence of nano-FeOx and nano-NiOx enriched the catalyst surface with extra oxygen moieties that counteracted the CO poisoning of the Pt substrate and electronically facilitated the kinetics of the FAOR, as revealed from CO stripping and impedance spectra.

A FeOx/NiOx/Pt catalyst was recommended for formic acid electro-oxidation; the essential anodic reaction in direct formic acid fuel cells.

Effect of mixed ZnO/CuO nanoparticles on the structural, morphological, and topographical properties

In the present work, pure and composite ZnO/CuO were effectively deposited by chemical spray pyrolysis. Structural, morphological, and topographical features have been well investigated and explained. XRD analysis showed a polycrystalline structure with hexagonal and monoclinic systems for ZnO and CuO, respectively. The crystal size that calculated from XRD patterns has decreased with the increase of CuO content, while the dislocation density and the micro strain have increased. These results lead to high defects in the structure of the nanocomposite which will be more efficient in a specific application. Moreover, the morphology of the samples was examined by FESEM and it was spherical-like shapes and has elevated points, whereas the EDX confirm the existence of the employed materials without any other undesired materials. The topography of the surface depicted a slightly rough surface which will be suitable for different nanoelectronics devices.