A green synthesis of “naked” Pt and PtPd catalysts for highly efficient methanol electrooxidation

Abstract

Up to now, green synthesis of "naked" nanoobjects with clean surfaces is still a great challenge since structure-directing agents such as surfactants are usually used to induce the anisotropic particle growth for interesting nanostructures in solution. Here, a green synthesis approach for preparing "naked" Pt nanoparticles (NPs) in acetic acid solution was reported. Interestingly, Pt NPs with different morphologies (well-defined polyhedrons, irregular polyhedron-constructed chain networks and nanoflower-constructed chain networks) could be successfully synthesized at different concentrations of acetic acid without adding additional structure-directing agents and reducing agents. The acetic acid itself works both as structure-directing agent and reducing agent for the formation of these interesting Pt NPs. Specifically; the synthesized NPs are "naked" with clean surfaces since the acetic acid is a weakly-capping agent which can be easily removed after the washing process. The versatility of this method is further demonstrated by preparation of "naked" PtPd alloy NPs. In particular, the as-prepared "naked" Pt _5.20 and Pt 3 Pd 1_5.20 NPs are demonstrated to be excellent catalysts with much higher electroactivity and better durability than the commercial Pt black catalyst (Hispec™ 1000) for the methanol oxidation reaction. The method reported in this work may pave the way for simple, low-cost, green and eco-friendly synthesis of "naked" metal catalysts for advanced electrocatalytic applications.

“Weakly Ligated, Labile Ligand” Nanoparticles: The Case of Ir(0)n·(H+Cl–)m

“…38−41 Solvent-only stabilized nanoparticles have been claimed in the literature, 42−46 but often anionic ligands (such as Cl – , OAc – , or other anions present in the synthetic precursor) are present but have not been tested, nor hence ruled out, as actual sources of nanoparticle stabilization. For example, in a recent report, 35 Pt(0) nanoparticles generated in acetic acid are claimed to be naked, but the high probability of surface OAc – as a stabilizing ligand was not tested nor ruled out. We discuss putatively naked nanoparticles more in the Supporting Information (SI) for the interested reader.…”

“…There have also been a number of reports attempting to prepare putatively “naked” nanoparticles that, in at least the literal interpretation of naked, would be devoid of any ligands, even solvent. ,− Although there have been claims of naked nanoparticles in the literature, − nanoparticle surfaces will of course never be truly naked in solution because even solvent-to-metal bond energies are 10 ± 3 kcal/mol for even the extreme case of metal–alkane bonds, at least in small-molecule organometallic complexes. − Solvent-only stabilized nanoparticles have been claimed in the literature, − but often anionic ligands (such as Cl – , OAc – , or other anions present in the synthetic precursor) are present but have not been tested, nor hence ruled out, as actual sources of nanoparticle stabilization. For example, in a recent report, Pt(0) nanoparticles generated in acetic acid are claimed to be naked, but the high probability of surface OAc – as a stabilizing ligand was not tested nor ruled out. We discuss putatively naked nanoparticles more in the Supporting Information (SI) for the interested reader.…”

Photocatalytic hydrogen generation from a visible-light responsive metal–organic framework system: the impact of nickel phosphide nanoparticles

“…In order to compare the performance of Ni2P/MIL-125-NH2 with Pt/MIL-125-NH2, we synthesized "naked" Pt NPs 48 with the size of ~19 nm (Fig. S28, S29).…”

Surfactant-free colloidal syntheses of precious metal nanoparticles for improved catalysts

“…This is typically achieved adding small-molecules (molar mass < 100 g mol -1 ) and/or gas molecules. 64,123 Halogen ions have also been reported as shape controlling agents. 264 In the polyol synthesis, such shape control was achieved for instance by using EG/DMSO, to obtain branched Pd nanowires.…”

“…114 Following the definition proposed above for surfactant-free syntheses, the use of ions such as citrate, 115,116 oxalate, 117 ascorbic acid, 118 most ionic liquids 119 as well as anions such as amino-acids or enzymes 120 is ruled out. However species such as acetate [121][122][123] or sulfate / phosphate, 124 formaldehyde or formic acid, 125 could be used but are also not considered further here to keep the focus on syntheses where the solvent is playing the triple role of reaction medium, reducing agent and stabilizer.…”