Elucidation of the mechanism for the alcohol electrochemical oxidation on Ni-based catalysts: an operando X-ray absorption spectroscopy approach.

In Recent years, we have investigated a series of Ni-based electrocatalysts for the alkaline oxygen evolution reaction (OER) and alcohol oxidations reactions (AOR). We have well-stablished that the catalytic activity trend for the OER is NiS2>Ni(OH)2>NiO=NiCo2O4. However, this trend is reversed for the AOR. Based on operando XAS, we have found that all catalysts reconstruct under OER conditions to form the actual catalytic species NiOOH; however, the higher catalytic activity of NiS2 for the OER has been correlated with a smaller Ni-O and Ni-Ni bond length of the in-situ formed NiOOH, which may result from the formation of Ni4+ species. These species have been suggested to play an important role in the AOR in a ‘potential-dependent oxidation’ mechanism proposed for Ni oxide-based catalyst, which contrasts a more traditional ‘indirect oxidation’ mechanism on NiOOH. In this context, we propose conducting operando XAS to gain insights into the formation of NiOOH during the ethanol oxidation reaction on NiS2, Ni(OH)2, NiO and NiCo2O4 electrodes. NEXAFS and EXAFS at the Ni K-edge will be measured to monitor the chemical and structural changes of the in-situ formed NiOOH under OER and EOR conditions, aiming to confirm the potential mechanism of EtOH oxidation in these Ni-based catalysts, and explain the catalytic activity trends observed in our studies.