Pb and Sb modified Pt/C catalysts for direct formic acid fuel cells

Pt Deposits on Bi-Modified Pt Electrodes of Nanoparticle and Disk: A Contrasting Behavior of Formic Acid Oxidation

This work presents a contrasting behavior of formic acid oxidation (FAO) on the Pt and Bi deposits on different Pt substrates. Using irreversible adsorption method, Bi and Pt were sequentially deposited on Pt electrodes of nanoparticle (Pt NP) and disk (Pt disk). The deposited layers of Bi and Pt on the Pt substrates were characterized with X-ray photoelectron spectroscopy, transmission microscopy and scanning tunneling microscopy. The electrochemical behaviors and FAO enhancements of Pt NP and Pt disk with deposited Bi only (i.e., Bi/Pt NP and Bi/Pt disk), were similar to each other. However, additional deposition of Pt on Bi/Pt NP and Bi/Pt disk (i.e., Pt/Bi/Pt NP and Pt/Bi/Pt disk) changed the electrochemical behavior and FAO activity in different ways depending on the shapes of the Pt substrates. With Pt/Bi/Pt NP, the hydrogen adsorption was suppressed and the surface oxidation of Pt was enhanced; while with Pt/Bi/Pt disk, the opposite behavior was observed. This difference was interpreted as a stronger interaction between the deposited Bi and Pt on Pt NP than that on Pt disk. The FAO performance on Pt/Bi/Pt NP is much better than that on Pt/Bi/Pt disk, most likely due to the difference in the interaction between the deposited Pt and Bi depending on the shapes of Pt substrates. In designing FAO electrochemical catalysts using Pt and Bi, the shape of a Pt substrate was concluded to be critically considered.

PT-BI Co-Deposit Shell on AU Nanoparticle Core: High Performance and Long Durability for Formic Acid Oxidation

This work presents the catalysts of Pt-Bi shells on Au nanoparticle cores and Pt overlayers on the Pt-Bi shells toward formic acid oxidation (FAO). Pt and Bi were co-deposited on Au nanoparticles (Au NP) via the irreversible adsorption method using a mixed precursor solution of Pt and Bi ions, and the amount of the co-deposits was controlled with the repetition of the deposition cycle. Rinsing of the co-adsorbed ionic layers of Pt and Bi with a H2SO4 solution selectively removed the Bi ions to leave Pt-rich and Bi-lean (<0.4 atomic %) co-deposits on Au NP (Pt-Bi/Au NP), conceptually similar to de-alloying. Additional Pt was deposited over Pt-Bi/Au NPs (Pt/Pt-Bi/Au NPs) to manipulate further the physicochemical properties of Pt-Bi/Au NPs. Transmission electron microscopy revealed the core–shell structures of Pt-Bi/Au NPs and Pt/Pt-Bi/Au NPs, whose shell thickness ranged from roughly four to six atomic layers. Moreover, the low crystallinity of the Pt-containing shells was confirmed with X-ray diffraction. Electrochemical studies showed that the surfaces of Pt-Bi/Au NPs were characterized by low hydrogen adsorption abilities, which increased after the deposition of additional Pt. Durability tests were carried out with 1000 voltammetric cycles between −0.26 and 0.4 V (versus Ag/AgCl) in a solution of 1.0 M HCOOH + 0.1 M H2SO4. The initial averaged FAO performance on Pt-Bi/Au NPs and Pt/Pt-Bi/Au NPs (0.11 ± 0.01 A/mg, normalized to the catalyst weight) was higher than that of a commercial Pt nanoparticle catalyst (Pt NP, 0.023 A/mg) by a factor of ~5, mainly due to enhancement of dehydrogenation and suppression of dehydration. The catalytic activity of Pt/Pt-Bi/Au NP (0.04 ± 0.01 A/mg) in the 1000th cycle was greater than that of Pt-Bi/Au NP (0.026 ± 0.003 A/mg) and that of Pt NP (0.006 A/mg). The reason for the higher durability was suggested to be the low mobility of surface Pt atoms on the investigated catalysts.

Pt Deposits on Bi/Pt NP Catalyst for Formic Acid Oxidation: Catalytic Enhancement and Longer Lifetime

This work presents an improvement in the activity and catalytic lifetime of Pt deposits on Bi-modified Pt nanoparticles (Bi/Pt NP) toward formic acid oxidation (FAO). Using an irreversible adsorption method, Bi was deposited on Pt NP to form Bi/Pt NP and sequentially Pt was deposited on Bi/Pt NP to form Pt/Bi/Pt NP. Voltammetric studies of Pt NP, Bi/Pt NP, and Pt/Bi/Pt NPs supported that Pt deposits of Pt/Bi/Pt NPs provided quite a unique behavior: simultaneous surface oxidation of deposited Pt and Bi and significant resistance to the oxidative removal of Bi. Furthermore, combined spectroscopic investigations revealed that the concentration of the employed Pt precursor ion solution determined the amount of deposited Pt from ∼0.2 to ∼0.4 in coverage. The best Pt/Bi/Pt NP catalyst with a Pt coverage of ∼0.25 enhanced the dehydrogenation processes below ∼0.4 V by a factor of more than 2 and increased the FAO current at ∼0.8 V roughly by 15 times, referring to those of Bi/Pt NP. The lifetime measurement works revealed that after the 1000th voltammetric cycle to 0.4 V, the FAO currents of Pt/Bi/Pt NPs were 2 and 4 times higher than those of Bi/Pt NP and Pt NP, respectively. The Pt deposits on Bi/Pt NP were concluded to play two roles in FAO: the promotion of FAO processes to increase the activity and the retardation of Bi oxidative removal to maintain the activity much longer.

Shape regulation of high-index facet nanoparticles by dealloying

Tetrahexahedral particles (~10 to ~500 nanometers) composed of platinum (Pt), palladium, rhodium, nickel, and cobalt, as well as a library of bimetallic compositions, were synthesized on silicon wafers and on catalytic supports by a ligand-free, solid-state reaction that used trace elements [antimony (Sb), bismuth (Bi), lead, or tellurium] to stabilize high-index facets. Both simulation and experiment confirmed that this method stabilized the {210} planes. A study of the PtSb system showed that the tetrahexahedron shape resulted from the evaporative removal of Sb from the initial alloy-a shape-regulating process fundamentally different from solution-phase, ligand-dependent processes. The current density at a fixed potential for the electro-oxidation of formic acid with a commercial Pt/carbon catalyst increased by a factor of 20 after transformation with Bi into tetrahexahedral particles.

One-step synthesis of ultrathin PtxPb nerve-like nanowires as robust catalysts for enhanced methanol electrooxidation

Ultrathin Pt_xPb nerve-like nanowires (NNWs) with a diameter of only around 3.6 nm were synthesized by a one-step wet-chemical strategy, and they served as robust catalysts for greatly enhancing methanol electrooxidation both under acidic and alkaline conditions. Due to the high CO-poisoning tolerance, superior electrocatalytic activity and stability endowed by the Pt-Pb alloyed composition and the unique structure, the Pt_3.5Pb NNWs showed the highest specific activity of 2.78 mA cm^-2 in acidic media and 6.51 mA cm^-2 in alkaline media toward the methanol oxidation reaction (MOR), which are 5.24 and 4.12 times higher than those of the commercial Pt/C catalysts, respectively. Meanwhile, the demonstrated synthetic strategy for Pt-Pb nanocrystals may stimulate more inspiration and strategies of the novel metal-based nanocrystals for promising applications in electrocatalysis.

Electrocatalysis of formic acid on palladium and platinum surfaces: from fundamental mechanisms to fuel cell applications

A brief overview is presented on recent progress in mechanistic studies of formic acid oxidation, synthesis of novel Pd- and Pt-based nanocatalysts and their practical applications in direct formic acid fuel cells.