Dissolution of Noble Metals during Oxygen Evolution in Acidic Media

Abstract

The electrochemical production of hydrogen and hydrocarbons is considered to play a decisive role in the conversion and storage of excess amounts of renewable energy. The electrocatalysis of the oxygen evolution reaction (OER), however, faces significant challenges for practical implementation of electrolyzers. In this work, a comparative study on the activity and stability of oxidized polycrystalline noble metals during the OER is presented. All studied metals exhibit transient and steady-state dissolution. Transient dissolution takes place during oxide formation and reduction. Steady-state dissolution depends on the OER mechanism on each surface: On metals such as Ru and Au, for which oxygen from the oxide participates in the OER, the Tafel slope is low and the dissolution rate is high. In contrast, on metals for which oxygen evolves directly from adsorbed water, such as Pt and presumably Pd, the Tafel slopes are high and the dissolution rates are low. This should be considered in the design of optimal OER catalysts.The conventional energy strategy based on the deployment of fossil fuels comprises two serious drawbacks: depletion of irretrievable fuels and environmental concerns upon their exploitation. As a consequence, the growing general interest in the concept of sustainable renewable energy has boosted the implementation of alternative energy supply technologies over recent years. [1] Particularly, the utilization of energy from sun and wind is considered as an adoptable scenario in the energy paradigm shift, as each of them is capable of covering the global energy demand, which is estimated to be 17 TW in 2030. [2] Unlike traditional energy supplies, however, the production of electricity from sun and wind is intermittent, which creates a terawatt-scale challenge: fluctuations in energy supply by variation of seasonal weather conditions must be efficiently leveled off. Consequently, besides production itself, conversion and storage of enormous amounts of energy during peak production hours as well as its constant distribution to end users during downtime is an essential piece of the puzzle. One approach capable of handling the terawatt scale is the conversion of electrical energy and storage in the form of chemical bonds as, for example, hydrogen (through water reduction) or hydrocarbons (through carbon dioxide reduction). [3] For instance, these fuels can be produced electrochemically in electrolyzers [4] and then utilized at local fuel cell factories or transported to consumers on demand. [5] The essential counterreaction in an electrolyzer for either technology (water or CO 2 reduction) will be the oxygen evolution reaction (OER). However, the high energy required for the rearrangement of the chemical bonds of water during the OER is actually a bottleneck in the production costs compared to other technologies such as reforming. [3a, 6] Namely, sluggish electrode kinetics and detachment of evolved gas bubbles can severely restrict efficiency. [7] Moreover, the catalyst activity needs to be sustained...

Standards and Protocols for Data Acquisition and Reporting for Studies of the Electrochemical Reduction of Carbon Dioxide

“…[43][44][45][46][47][48] The transition metal cations evolved from the anode can reach the cathode even when an anion exchange membrane is utilized to separate the electrode chambers. 49 Whether this crossover occurs during operation or during the storage and cleaning of the electrochemical cell has yet to be resolved conclusively.…”

Benchmarking the Stability of Oxygen Evolution Reaction Catalysts: The Importance of Monitoring Mass Losses

“…It should also be noted that corrosion mechanisms are highly dependent on the material. [39] The degradation of some materials may actually be accelerated by potential cycling (as shown by Mayrhofer and co-workers to be the case for Pt, by combining cyclic voltammetry with online ICP measurements [61] ). Consequently, to study the resistance to corrosion of such materials, potentiodynamic-rather than potentiostatic-tests would be necessary.…”

“…On the other hand, macroscopic techniques can be applied to determine the corrosion rates; these include the rotating ring disk electrode (RRDE; for example, for monitoring the anodic dissolution of RuO 2 [36,37] ), the quartz crystal microbalance, [38] and inductively coupled plasma mass spectrometry (ICP-MS). [39][40][41] Nonetheless, as of yet, no standardized protocols for assessing the stability under OER conditions have emerged.…”

Bulk-Palladium and Palladium-on-Gold Electrocatalysts for the Oxidation of Hydrogen in Alkaline Electrolyte

“…1a. 41,42 Having quantified the Pd PC -RF in acid medium, the same electrode was transferred to a solution of Ar-saturated 0.1 M NaOH, where we proceeded to record new CVs between ≈0.4 and ≈1.0-1.3 V RHE . The resulting voltammograms with different E inversion values appear plotted in Figure 1c, while Figure 1d shows a direct comparison between the individual CVs recorded in both electrolytes using an inversion potential of ≈1.0 V RHE .…”

“…Such excursions to high potentials reportedly result in significant gold-dissolution and re-deposition following the oxidation and reduction of the disc's surface, respectively. 68,42 Having attained a stable Au PC -surface state and quantified its RF, we proceeded to transfer the electrode to a deaerated solution of 0.1 M H 2 SO 4 with ≈1 mM CuSO 4 , holding the potential at ≈0.75 V RHE in order to prevent uncontrolled copper-deposition on its surface. The Cu upd process was first studied by recording CVs between this positive potential limit and different negative inversion potentials of ≈0.31, ≈0.29, ≈0.27, ≈0.25 and ≈0.23 V RHE .…”