Highlights

The chemistry of electrocatalytic oxygen evolution over Iridium

By using pulse voltammetry, operando X-ray absorption and photoelectron spectroscopy (XAS, XPS) measurements together with DFT calculations on iridium oxide we show that the applied bias does not act directly on the reaction coordinate, but affects the electrocatalytically generated current through charge accumulation in the catalyst. We find that the logarithm of the rate of OER linearly correlates with the charge accumulated. The applied potential drives the formation of empty Ir 5d states, ascribed to formally Ir⁵⁺ species, and the concomitant appearance of electron-deficient oxygen surface species (μ1-O and μ2-O) that are responsible for water activation and oxidation.

Using confined electrolyte for elecrochemical in situ studies

Electrocatalysis can use electrical power sources to accelerate chemical reactions, The interface between an (electro-)catalyst and a liquid electrocatalyte is essential to these processes. In order to understand the chemistry at these interfaces, we turn to surface-sensitive X-ray s[ectroscopy. However, air or thin layers of liquid would block the photoelectrons we wan to measure.
We tackled that problem by using an atomically thin window, namely graphene. It is transparent to the incoming radiation and the outcoming electrons. It is also an evaporation barrier, which leads to confined electrolyte, even in vacuum. With this method we now succesfully study the solid liquid interface during electrochemistry. more

In situ investigation of CO2RR on copper oxide based electrocatalyst

In situ investigation of CO₂RR on copper oxide based electrocatalyst

The electroreduction of CO₂ to valuable hydrocarbons and alcohols was investigated in accurately prepared copper oxidation states (Cu⁰, Cu⁺ and Cu²⁺) electrodes. By combining advanced X-ray spectroscopy and in situ micro-reactors it was found that the surface, sub-surface and bulk properties of the electrochemically prepared catalysts are dominated by the formation of copper carbonates on the surface of cupric-like oxides, which prompts catalyst deactivation by restraining effective charge transport. In addition, the formation of reduced or partially-reduced copper catalysts yields the key dissociative proton-consuming reactive adsorption.
This investigation was performed in close collaboration with the “Interface Science” department led by Prof. Roldan-Cuenya. more

Graphene membranes for Electrochemical Operando X‑ray Spectroscopy and Scanning Electron Microscopy

NAPXPS is operated in the soft X-ray regime at a partial pressure up to a few mbars. Taking into account these experimental limitations, the in situ/operando electrochemical experiments are performed typically using a solid oxide electrolytes operated at high temperature or with ionomeric membranes operated at room temperature. In order to improve the wetting of the ionomeric membrane, it is back-filled with a aqueous electrolyte. This approach allows for an optimal membrane hydration, enabling the transport of ions but not electrons. The performance of this approach is boosted adding a photoelectron transparent graphene onto the electrode/ionomeric membranes assemble. This is a suitable approach to improve the stability of the free standing graphene (the ionomeric membrane holds the pressure difference) and the evaporation of water (the graphene cover is an evaporation barrier). This approach is fully compatible with ESEM allowing the correlative investigation of the same electrode by means of in situ/operando electron-spectroscopy and electron-microscopy. more

Correlating in situ electron microscopy and in situ X-ray spectroscopy investigation of CO2 electroreduction on copper oxide based electrocatalyst

Correlating in situ electron microscopy and in situ X-ray spectroscopy investigation of CO₂ electroreduction on copper oxide based electrocatalyst

By combining in situ surface- and bulk-sensitive X-ray spectroscopies with electrochemical scanning electron microscopy, the variation in the morphology and electronic structure of copper during the lectroreduction of CO₂ into valuable hydrocarbons and alcohols was revealed. It was found that the electrified interface surface and near[1]surface are dominated by reduced copper. The selectivity to the formation of the key C−C bond is enhanced at higher cathodic potentials as a consequence of increased copper metallicity. Furthermore, the reduction of the copper oxide electrode and oxygen loss in the lattice yields the electrode reconstruction inducing the formation of a the electrode to yield a rougher surface with more uncoordinated sites. more