Excellent Electroactivity of Ternary Pd–Ag–Sn Nanocatalysts for Ethanol Oxidation

Designing New Material Based on Functionalized Multi-Walled Carbon Nanotubes and Cu(OH)2–Cu2O/Polypyrrole Catalyst for Ethanol Oxidation in Alkaline Medium

In this work, copper(II) hydroxide (Cu(OH)2) and copper oxide (Cu2O) nanostructures are deposited on functionalized multi-walled carbon nanotubes/polypyrrole to report an efficient electrocatalyst for ethanol oxidation in alkaline medium. In the first step, the deposition of functionalized multi-walled nanotubes of carbon (F-MWCNTs) on the electrode surface was carried out using drop casting mode followed by the electrodeposition of polypyrrole (PPy) and copper nanoparticles (Cu-Nps) using galvanostatic mode. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed in order to study the morphology and the structure of the elaborated catalysts. Electrochemical characterization conducted by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) revealed that the introduction of functionalized multi-walled carbon nanotubes enhances the electric properties of the nanocomposites and offers a large active surface area. The prepared electrocatalyst was then tested in a solution of 0.1 M NaOH containing 0.2 M of ethanol showing high performance (7 mA cm−2 at 0.85 V vs Ag/AgCl) and good stability (over 1800 s) toward ethanol oxidation.

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.

Designing Robust Support for Pt Alloy Nanoframes with Durable Oxygen Reduction Reaction Activity

Polymer electrolyte membrane fuel cells are appealing to resolve the environmental and energy issues but are still heavily inhibited by the dilemma of fabricating effective and durable electrocatalysts for oxygen reduction reaction (ORR). In this work, highly open Pt₃Cu nanoframes and one-dimensional, hollow titanium nitride architectures are both successfully explored and implemented as the new system to replace the traditional Pt-carbon motif. The ORR performance of the obtained electrocatalyst shows specific and mass activities of 5.32 mA cm^-2 and 2.43 A mg_Pt^-1, respectively, which are 14.4 and 11.6 times higher than those of the commercial Pt/C. Notably, the novel catalyst also exhibits high stability and a much slower performance degradation than that of the benchmarked Pt₃Cu/C with the same durability testing procedures. The comprehensive data confirm that the new type of catalyst possesses a high charge transfer during the ORR process, and the unique structure and synergistic effects between anchored Pt and the support mainly contributes to the high stability. This work provides a strategic method for designing an effective ORR electrocatalyst with desirable stability.

Monodisperse ordered indium-palladium nanoparticles: synthesis and role of indium for boosting superior electrocatalytic activity for ethanol oxidation reaction

The slow kinetics of ethanol oxidation reaction (EOR) has limited its widespread use for fuel cells. Bimetallic catalysts with optimized surface compositions can considerably govern rate-determining steps through selectivity for CH3COOH formation or by facilitating the adsorption of OHadsvia the bifunctional effect of an alloy to increase the EOR's kinetic rates. Here, we reported monodisperse ordered In-Pd nanoparticles as new bimetallic high-performance catalysts for EOR. In-Pd nanoparticles, i.e., In3Pd2 and In3Pd5 were prepared using arrested precipitation in solution, and their composition, structures, phase and crystallinity were confirmed using a variety of analyses including TEM, XPS, EDS and XRD. In-Pd nanoparticles were loaded on carbon black (Vulcan XC-72) as electrocatalysts for EOR in alkaline media. In3Pd2 and In3Pd5 nanoparticles exhibited 5.8 times and 4.0 times higher mass activities than commercial Pd/C, which showed that the presence of indium greatly boosts electrocatalytic reactivity for EOR of Pd catalysts. This performance is the best among those of bimetallic nanoparticles reported to date. Such high performance of In-Pd nanoparticles may be attributed to the following two reasons. First, In-Pd nanoparticles exhibited excellent CO anti-poison ability, as confirmed by CO striping experiments. Second, as revealed by DFT calculations of metals with OHads adsorption, In atoms on In3Pd2 surface exhibited the lowest energy (-1.659 eV) for OHads adsorption as compared to other common oxophilic metals including Sn, SnPt, Ag, Ge, Co, Pb, and Cu. We propose that the presence of indium sites promoted efficient free OH radical adsorption on indium sites and resulted in a faster reaction rate of acetate formation from acetaldehyde (the rate determining step for EOR on Pd sites). Finally, a single direct ethanol fuel cell (DEFC) with Pd/C anode was prepared. Compared to the results for a commercial Pd/C anode, the open circuit voltage (OCV) of In3Pd2/C improved by 0.25 V (from 0.64 to 0.89 V) and the power density improved by ∼80% (from 3.7 to 6.7 mW cm-2), demonstrating its practical uses as Pt or Pd catalyst alternatives for DEFC.