Co-Based Mesoporous Spinels for Oxygen Evolution Reaction in Alkaline Medium
Authors: Habrioux Aurélien , Abidat Ismail , Canaff Christine , Morais Claudia , Comminges Clément , Napporn Teko W. , Kokoh Kouakou Boniface 
Published: February 2020

Stabilization of atmospheric CO2amount in the upcoming years requires a transition towards a new energetic grid involving the large scale use of renewable resources. As these energies are intermittent, it is required to implement costly effective and efficient electricity storage systems. These latter systems will allow converting intermittent renewable energies into sustainable energetic vectors (hydrogen, electron). For this purpose, the oxygen evolution reaction (OER) plays an important role. OER possesses a sluggish kinetics that can be enhanced by using a catalyst exhibiting reliable surface composition and morphostructural properties. Additionally, in order to limit the use of scarce noble metals, the synthesis of efficient 3d transition metal oxide-based catalysts is of interest. Such materials are thermodinamically stable in alkaline media. These materials are known to be capable of improving the OER kinetics in alkaline medium.
As activity and stability of materials depend on their composition and morphostructural properties, the synthesis of well-defined catalysts is of utmost importance. This can be achived by synthesizing materials using nanocasting approach. In this presentation, oxygen deficient NixCo3-xO4-δ materials have been synthesized by replicating ordered mesoporous silica templates (KIT-6, SBA-15). Materials have been investigated using numerous physico-chemical techniques such as X-ray induced photoelectron spectroscopy, high resolution transmission electron microscopy, X-ray diffraction and Raman spectroscopy. Evidences from XPS and Raman measurements reveal that the different catalysts surface is hydroxylated. A particular attention has been carried out to restructuring phenomena occurring upon potential cycling and responsible for greatly improving the OER activity of the material. These surface restructuring phenomena have been characterized using post-mortem Raman and X-ray induced photoelectron spectroscopies. It was observed that the intrinsic activity of the different restructured catalysts depends on the incorporated amount of nickel and correlates with CoIII/CoIV peak potential. The modulation of CoIII/CoIV peak potential is explained by changes in the chemical environment of surface Co atoms and probably results in the formation of a layered mixed nickel/cobalt oxyhydroxyde. Nickel modulates the electronic properties of the Co active site, which modifies adsorption energies of key oxygenated intermediates and allows improving the OER activity of catalysts. It can be moreover noticed that catalysts described in this presentation are among the most active materials ever reported to date. For some of them, after surface restructuring, the overpotential at 10 mA.cm-2 is in fact as low as 310 mV. These results are of utmost importance for the development of active catalysts towards OER in alkaline medium. This is at the heart of the key for the development of new electrochemical energy conversion devices using hydrogen as energy vector.

Figure 1