Explanation of Dramatic pH-Dependence of Hydrogen Binding on Noble Metal Electrode: Greatly Weakened Water Adsorption at High pH
Hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) are both 2 orders slower in alkaline electrolyte than in acidic electrolyte, but no explanation has been provided. The first step toward understanding this dramatic pH-dependent HOR/HER performance is to explain the pH-dependent hydrogen binding to the electrode, a perplexing behavior observed experimentally. In this work, we carried out Quantum Mechanics Molecular Dynamics (QMMD) with explicit considerations of solvent and applied voltage (U) to in situ simulate water/Pt(100) interface in the condition of under-potential adsorption of hydrogen (HUPD). We found that as U is made more negative, the electrode tends to repel water, which in turn increases the hydrogen binding. We predicted a 0.13 eV increase in hydrogen binding from pH = 0.2 to pH = 12.8 with a slope of 10 meV/pH, which is close to the experimental observation of 8 to 12 meV/pH. Thus, we conclude that the changes in water adsorption are the major causes of pH-dependent hydrogen binding on a noble metal. Furthermore, the new insight of critical role of surface water in modifying electrochemical reactions provides a guideline in designing HER/HOR catalyst targeting for the alkaline electrolyte.
- Research Organization:
- California Institute of Technology (CalTech), Pasadena, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- Grant/Contract Number:
- SC0004993
- OSTI ID:
- 1467598
- Journal Information:
- Journal of the American Chemical Society, Vol. 140, Issue 25; ISSN 0002-7863
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Similar Records
Understanding the pH Dependence of Underpotential Deposited Hydrogen on Platinum
pH Effects on Hydrogen Evolution and Oxidation over Pt(111): Insights from First-Principles