Sub-4 nm PtZn Intermetallic Nanoparticles for Enhanced Mass and Specific Activities in Catalytic Electrooxidation Reaction

Abstract

Atomically ordered intermetallic nanoparticles (iNPs) have sparked considerable interest in fuel cell applications by virtue of their exceptional electronic and structural properties. However, the synthesis of small iNPs in a controllable manner remains a formidable challenge because of the high temperature generally required in the formation of intermetallic phases. Here we report a general method for the synthesis of PtZn iNPs (3.2 ± 0.4 nm) on multiwalled carbon nanotubes (MWNT) via a facile and capping agent free strategy using a sacrificial mesoporous silica (mSiO) shell. The as-prepared PtZn iNPs exhibited ca. 10 times higher mass activity in both acidic and basic solution toward the methanol oxidation reaction (MOR) compared to larger PtZn iNPs synthesized on MWNT without the mSiO shell. Density functional theory (DFT) calculations predict that PtZn systems go through a "non-CO" pathway for MOR because of the stabilization of the OH* intermediate by Zn atoms, while a pure Pt system forms highly stable COH* and CO* intermediates, leading to catalyst deactivation. Experimental studies on the origin of the backward oxidation peak of MOR coincide well with DFT predictions. Moreover, the calculations demonstrate that MOR on smaller PtZn iNPs is energetically more favorable than larger iNPs, due to their high density of corner sites and lower-lying energetic pathway. Therefore, smaller PtZn iNPs not only increase the number but also enhance the activity of the active sites in MOR compared with larger ones. This work opens a new avenue for the synthesis of small iNPs with more undercoordinated and enhanced active sites for fuel cell applications.

A Comprehensive Review on Controlling Surface Composition of Pt‐Based Bimetallic Electrocatalysts

“…By adjusting the reaction temperature, Pt-covered bimetallic nanomaterials could be obtained. [85][86][87] For example, by controlling the amount of cetyltrimethylammonium chloride and Co(acac) 2 , Pt-rich facets and ordered intermetallic hierarchical Pt 3 Co nanowires could be obtained. A good www.advenergymat.de www.advancedsciencenews.com example is that during the preparation of PtPb nanoparticles progress, when ascorbic acid is applied as reducing agent to replace phenol, PtPb nanoplate with ≈1.0 nm Pt shell thickness could be obtained.…”

Phase Modulating of Cu–Ni Nanowires Enables Active and Stable Electrocatalysts for the Methanol Oxidation Reaction

“…To date, Pt‐based catalysts are regarded as primarily alternative catalysts for the MOR, although high costs and sluggish kinetics are vital factors to hamper their wide commercialization . In addition, the unsatisfied stability with a tendency to aggregate as well as poor tolerance to CO or other carbonaceous intermediates are tremendous problems in methanol oxidation . Searching for advanced candidates with both highly activity and stability becomes extremely meaningful.…”

Unusual Effect of Trace Water on the Structure and Activity of NixCo1−x Electrocatalysts for the Methanol Oxidation Reaction

“…The oxidation of methanol molecules and intermediates is more likely to take place on the (1 1 1) plane than on other crystal planes . Therefore, DFT calculations were performed to calculate methanol electrooxidation reactions on (1 1 1) crystal planes of the three alloys according to previous procedures . The optimal reaction pathway of the three structures (Figure b) shows that CH 3 O*→CH 2 O* is a potential limiting step.…”

“…When this step is thermodynamically possible under external potentials, one has the equilibrium Δ G +e U =0, and the corresponding U value is the limiting potential of this step. The Gibbs energy of each species was calculated by considering the entropic correction and solvation correction as reported before …”