Continuous Mesoporous Pd Films by Electrochemical Deposition in Nonionic Micellar Solution

Abstract

Mesoporous metals that combine catalytic activity and high surface area can provide more opportunities for electrochemical applications. Various synthetic methods, including hard and soft templating, have been developed to prepare mesoporous/nanoporous metals. Micelle assembly, typically involved in soft-templates, is flexible and convenient for such purposes. It is, however, difficult to control, and the ordering is significantly destroyed during the metal deposition process, which is detrimental when it comes to designing precisely mesostructured materials. In the present work, mesoporous Pd films were uniformly electrodeposited using a nonionic surfactant, triblock copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), as a pore-directing agent. The interaction between micelles and metal precursors greatly influences the metal growth and determines the final structure. The water-coordinated species interact with the ethylene oxide moiety of the micelles to effectively drive the Pd(II) species toward the working electrode surface. From small-angle neutron scattering data, it is found that spherical P123 micelles, with an average diameter of ∼14 nm, are formed in the electrolyte, and the addition of Pd ions does not significantly modify their structure, which is the essence of the micelle assembly approach. The uniformly sized mesopores are formed over the entire mesoporous Pd film and have an average pore diameter of 10.9 nm. Cross-sectional observation of the film also shows mesopores spanning continuously from the bottom to the top of the film. The crystallinity, crystal phase, and electronic coordination state of the Pd film are also confirmed. Through this study, it is found that the optimized surfactant concentration and applied deposition potential are the key factors to govern the formation of homogeneous and well-distributed pores over the entire film. Interestingly, the as-prepared mesoporous Pd films exhibit superior electrocatalytic activity toward the ethanol oxidation reaction by fully utilizing the accessible active surface area. Our approach combines electrochemistry with colloidal and coordination chemistry and is widely applicable to other promising metals and alloy electrocatalysts.

Nonsiliceous Mesoporous Materials: Design and Applications in Energy Conversion and Storage

“…The growth of Au crystals can be precisely controlled using electrochemical deposition . The crystallinity of Pd can also be improved using electrochemical deposition; the electrocatalytic activity is increased as a result . A mesoporous structure also increases the electroconductive and catalytic activity of other noble metals.…”

Designed Patterning of Mesoporous Metal Films Based on Electrochemical Micelle Assembly Combined with Lithographical Techniques

“…Besides Au, other mesoporous metal and alloy films have also been reported by using the corresponding metal species . Mesoporous Pd and PdCu films exhibited uniformly sized pores as well as large electrochemically active surface area (ECSA) . The mesoporous Pd film showed 5.4 and 2.4 times greater ethanol oxidation reaction (EOR) than the nonporous Pd film and Pd black (PdB), respectively, while the mesoporous PdCu film also showed more than twice the EOR of PdB.…”

Electrochemical preparation system for unique mesoporous hemisphere gold nanoparticles using block copolymer micelles

“…nanoparticles [11][12][13] and lms [14][15][16][17] with different metal compositions. The metals with mesoporous structures demonstrate superior catalytic activity per weight or surface area over their nonporous bulk forms.…”

“…The metals with mesoporous structures demonstrate superior catalytic activity per weight or surface area over their nonporous bulk forms. Previously, our group reported a severalfold increase in the catalytic activity of mesoporous metals in reactions such as the methanol oxidation reaction (MOR), 14,15 ethanol oxidation reaction (EOR), 13,[15][16][17] and nitric oxide reduction 12 as compared to their bulk nanoparticles and lms. Such improvement in the catalytic activity of mesoporous structures is mainly attributed to their signicantly larger surface areas, more exposed catalytically active sites, and increased durability against aggregation.…”

“…[25][26][27][28][29][30] Most of the papers on mesoporous metal structures synthesized by electrochemical deposition have utilized Au or Pt substrates due to its chemical stability and high electrical conductivity. [14][15][16][17] Fig. S6 † shows the amperometry (i-t) curves during the deposition of MHAuNPs (black dots) on a Ti/Si substrate and mesoporous gold lms (red dots) on an Au substrate at the same deposition condition.…”