Question

Reduction potential of hydrogen electrode is negative if

Answer 1

Photoelectrochemical cells

Michael Grätzel

nature 414 (6861), 338, 2001

Abstract Until now, photovoltaics—the conversion of sunlight to electrical power—has been dominated by solid-state junction devices, often made of silicon. But this dominance is now being challenged by the emergence of a new generation of photovoltaic cells, based, for example, on nanocrystalline materials and conducting polymer films. These offer the prospect of cheap fabrication together with other attractive features, such as flexibility. The phenomenal recent progress in fabricating and characterizing nanocrystalline materials has …

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Catalytic effect of platinum on oxygen reduction an ab initio model including electrode potential dependence

Alfred B Anderson, Titus V Albu

Journal of The Electrochemical Society 147 (11), 4229-4238, 2000

The effects of bonding to a platinum atom are calculated for the reduction of oxygen to water. The electron‐correlation corrected MP2 method is used, and the electrode potential is modeled by variations in values for the electron affinities of the reaction centers. Potential‐dependent transition state structures and activation energies are reported for the one‐electron reactions Formula [i] Formula [ii] Formula [iii] Formula [iv] This is the predicted lowest energy pathway. An alternative, where step (ii) is replaced by Formula [v] is excluded by the high activation energy calculated for it, though reduction of Pt‒O to Pt‒OH Formula [vi] has a very low activation energy. Compared to uncatalyzed outer‐Helmholtz‐plane values, bonding to the Pt has the effect of decreasing the calculated high reduction activation energies for Formula and Formula. Bonding to Pt also decreases the HOO· and increases the HO· activation energy values. The reverse reaction, oxidation of Formula to Formula, is also discussed in light of these results. The issues of potential‐dependent double‐layer potential drops and adsorbate bond polarizations are discussed, and it is pointed out that the results of this study can be used to estimate the effects of such potential drops.© 2000 The Electrochemical Society. All rights reserved.

Answer 2

Absolute electrode potential for an electorde cannot be measured without forming a cell. Therefore, people choose hydrogen as a standard reference, and define its electrode potential as 0. Then, with this reference, the electrode potentail of other electrodes can be measured, which is essential to electrochemistry.