Abstract
The effect of alloying with transition metals (Ni, Co, Fe) on the adsorption strength of phosphoric acid on Pt alloy surfaces was investigated using electrochemical analysis and first-principles calculations. Cyclic voltammograms of carbon-supported Pt3M/C (M = Ni, Co, and Fe) electrocatalysts in 0.1 M HClO4 with and without 0.01 M H3PO4 revealed that the phosphoric acid adsorption charge density near the onset potential on the nanoparticle surfaces was decreased by alloying with transition metals in the order Co, Fe, Ni. First-principles calculations based on density functional theory confirmed that the adsorption strength of phosphoric acid was weakened by alloying with transition metals, in the same order as that observed in the electrochemical analysis. The simulation suggested that the weaker phosphoric acid adsorption can be attributed to a lowered density of states near the Fermi level due to alloying with transition metals.
Highlights
When phosphoric acid is added to electrolytes, the electrocatalyst surface will be significantly adsorbed by phosphoric acid and its anions[6], which typically decreases the oxygen reduction reaction (ORR) activity[4, 5]
As the peak at −0.05 V (Pt) surfaces are totally covered at relatively low electrode potentials, the ORR activity determined at 0.85 V may be that at the maximum phosphoric acid coverage
density functional theory (DFT) calculations predicted weaker adsorption of phosphoric acid with alloying by Co, Fe, or Ni in the subsurface layers. Both the experimental and theoretical results revealed that the Pt alloyed with Ni showed the weakest adsorption of phosphoric acid, followed by the alloys with Fe and Co, and pure Pt
Summary
When phosphoric acid is added to electrolytes, the electrocatalyst surface will be significantly adsorbed by phosphoric acid and its anions[6], which typically decreases the ORR activity[4, 5]. The Pt(111) surfaces showed a higher potential at the maximum H2PO4,ad coverage (around 0.7 V vs RHE)[7]. As the Pt surfaces are totally covered at relatively low electrode potentials, the ORR activity determined at 0.85 V may be that at the maximum phosphoric acid coverage. As the Pt(100) facet is fully covered by phosphoric acid anions at a more negative potential (around 0.3 V vs RHE)[5], the phosphoric acid coverage of the Pt(100) facet at 0.6 V is considered hard to change. To decrease the phosphoric acid coverage on the Pt(111) facet, it is considered necessary to decrease the adsorption strength of phosphoric acid on the Pt(111) facet, as the equilibrium coverage at a certain potential is decreased by decreasing the adsorption strength of phosphoric acid[9]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
