In nano-sized FeWO<sub>4</sub> electrode material, both Fe and W metal cations are
suspected to be involved in the fast and reversible Faradaic surface
reactions giving rise to its pseudocapacitive signature. As for any
other pseudocapacitive materials, to fully understand the charge storage
mechanism, a deeper insight into the involvement of the electroactive
cations still has to be provided. The present paper illustrates how
operando X-ray absorption spectroscopy (XAS) has been successfully used
to collect data of unprecedented quality allowing to elucidate the
complex electrochemical behavior of this multicationic pseudocapacitive
material. Moreover, these in-depth experiments were obtained in real
time upon cycling the electrode, which allowed investigating the
reactions occurring in the material within a realistic timescale, which
is compatible with electrochemical capacitors practical operation. Both
Fe K-edge and W L<sub>3</sub>-edge measurements point out the involvement of the
Fe<sup>3+</sup>/Fe<sup>2+</sup> redox couple in the charge storage while W<sup>6+</sup> acts as a
spectator cation. The result of this study enables to unambiguously
discriminate between the Faradaic and capacitive behavior of FeWO4.
Beside these valuable insights toward the full description of the charge
storage mechanism in FeWO<sub>4</sub>, this paper demonstrates the potential of
operando X-ray absorption spectroscopy to enable a better material
engineering for new high capacitance pseudocapacitive electrode
materials.
Probing Structural Evolution and Charge Storage Mechanism of NiO2
H
x
Electrode Materials using In Operando Resonance Raman Spectroscopy
