Explicitly, the NiO concentration is relatively higher close to the surface of the catalyst particles.
We see that NiO is found in higher concentration close to the surface of the catalyst particles.
Larger crystallites of a higher purity ZrO2 phase where there is high concentration of ZrO2 (near the surface of the catalyst particles hotspots of this material).
As is clear in Fig. 1, the ZrO2 map shows an egg-shell distribution (only present at/close to the surface of the catalyst particles).
Since heterogeneously catalyzed reactions occur on the surface of the catalyst, the rates of such reactions are proportional to the accessible surface area of the catalyst.
This created an economic dilemma: graphite forms in layers on the surface of the catalyst, and at a certain point, causes it to deactivate, or stop working.
The amorphous and organised form of coke was found on the surface of the catalyst.
After initial reduction (Fig. 1b iii), the Cu spectra show the presence of both Cu+ and Cu0, which indicates that the surface of the catalyst was reduced to Cu.
It is also implied that particles that are rich in CexZr1−xO2 are less prone to graphite formation; in these particles, the CexZr1−xO2 forms a protective layer near the surface of the catalyst particles.
However, the phase distribution maps of NiO, NiAl2O4 and CexZryO2 revealed that NiO is mainly present near the surface of the catalyst particles (where the most of the CexZryO2 phases are present) while NiAl2O4 is closer to their core.
For these reasons, direct and unambiguous confirmation of the presence of Cu+ at the surface of the catalyst remains an ongoing opportunity for further advances in the field of Cu-based electrocatalysis and model development.
