| Generalized adsorption isotherm, 0.1 M HClO₄ | ω = 38.2 kJ mol⁻¹, corresponding to g = +15.4 |
|---|---|
| Cyclic voltammetry, 0.1 M HClO₄, 25–49 °C in 3 °C increments | As the temperature increased from 25 °C to 34 °C, peak II shifted to a lower potential; peak I maintained its position up to 34 °C, then shifted towards lower potentials beyond 34 °C |
| ΔG°, 0.1 M HClO₄ | Hydrogen adsorption became less spontaneous, with less negative ΔG° values, with increasing temperature |
| ΔS°, 0.1 M HClO₄ | ΔS° ≈ −55 J mol⁻¹ K⁻¹; as hydrogen coverage increased from 0.3 to 0.6, ΔS° shifted from −63 to −42 J mol⁻¹ K⁻¹ |
| ΔH°, 0.1 M HClO₄ | ΔH° remained negative across the entire coverage range and changed from −43.91 to −25.90 kJ mol⁻¹ as hydrogen coverage increased from 0.3 to 0.6 |
| ΔG°, 0.1 M HClO₄, 0.09 M HClO₄ + 0.01 M H₂SO₄, and 0.1 M H₂SO₄ | Less negative values were observed in pure H₂SO₄ and more negative values in pure HClO₄ |
| ΔS°, 0.1 M HClO₄, 0.09 M HClO₄ + 0.01 M H₂SO₄, and 0.1 M H₂SO₄ | ΔS° values were negative across all electrolytes; the magnitude became less negative with increasing hydrogen coverage, and the extent of ordering increased in the order HClO₄ < 0.09 M HClO₄ + 0.01 M H₂SO₄ < 0.1 M H₂SO₄ |
| ΔH°, 0.1 M HClO₄ and 0.1 M H₂SO₄ | ΔH° was more negative in H₂SO₄, while ΔG° was less negative than in HClO₄ |
| Cyclic voltammetry, 0.1 M NaOH and 0.1 M KOH | Hydrogen adsorption/desorption peaks shifted to a lower potential in NaOH than in KOH |
| Thermodynamic parameters, 0.1 M NaOH and 0.1 M KOH | ΔG° was slightly more negative in KOH; ΔS° and ΔH° were more negative in NaOH |
| Concentration dependence, 0.1–0.5 M HClO₄ | ΔG°, ΔS°, and ΔH° became less negative with increasing HClO₄ concentration |
| Concentration dependence, 0.05–1 M H₂SO₄ | ΔG° became less negative, ΔS° indicated enhanced interfacial ordering, and ΔH° became more negative with increasing H₂SO₄ concentration |
| Concentration dependence, 0.1 M and 0.3 M KOH | ΔG°, ΔS°, and ΔH° became less negative at the higher KOH concentration |
| Thermodynamic parameters, 0.1 M NaOH, 0.1 M HClO₄, and 0.1 M NaClO₄ | ΔG° was most favorable in NaOH and least favorable in NaClO₄; the magnitude of ΔS° followed NaOH > NaClO₄ > HClO₄; ΔH° was most exothermic in NaOH, followed by NaClO₄ and HClO₄ |
| TΔS° contribution | The TΔS° term ranged from 40–60 % of the ΔH° term |
Veenu Dalal, Chinmoy Ranjan. “The enthalpy–entropy tug-of-war in Pt-hydrogen adsorption: Reconciling bond strength and interfacial order.” ChemRxiv (). https://doi.org/10.26434/chemrxiv.15007886/v1
Values presented only in plots or images in the main paper or supporting information were not transcribed