Two Orders of Magnitude Enhancement in Oxide Ion Conductivity in Cu ₂ P ₂ O ₇ via Vanadium Substitution: A Pathway Toward SOFC Electrolytes

In the quest for green energy, Solid Oxide Fuel Cells (SOFC) have drawn considerable attention for chemical-to-electric energy conversion. Electrolyte materials with high oxygen ionic conductivity are essential for efficient SOFC operation. However, materials with higher oxygen ionic conduction are rare in nature. Selective chemical substitution is an effective route to enhance the ionic conductivity of existing materials. In the present paper, we report the enhancement of the ionic conductivity of Cu2P2–xVxO7 by vanadium substitution. The electrical (direct current (dc) and alternating current (ac) conductivity, diffusivity, hopping rate, electric modulus, and dielectric properties) and crystal structural properties of Cu2P2–xVxO7 (x = 0, 0.4, 0.6, 0.8, and 1) are investigated by impedance spectroscopy and neutron diffraction, respectively. X-ray photoelectron spectroscopy (XPS) study confirms the presence of Cu2+, P5+, and V5+ monovalent states. The dc conductivity results reveal a 2 orders of magnitude enhancement of ionic conductivity from ∼3.81 × 10–5 S cm–1 for x = 0 to ∼2.08 × 10–3 S cm–1 for x = 1 at 993 K, revealing a possible application in SOFCs. DC transport number studies reveal that the total conductivity is dominated by ionic conduction (>95%). In addition, the diffusivity and hopping rate of the oxide ions increase with increasing x. Besides, the ac conductivity, electric modulus, and dielectric properties have been investigated to illustrate the microscopic conduction mechanism. The derived results suggest that the mechanism for ionic conduction is the correlated barrier hopping (CBH) process. Soft-bond valence sum (BVS) analysis of the neutron diffraction patterns reveals three-dimensional (3D) oxide ion conduction pathways within the crystal structure. The crystal structure study reveals an increase in the unit cell volume, polyhedra volume, and polyhedral distortion with increasing x, which leads to an enhancement of the ionic conduction. The present study provides a pathway to enhance the ionic conductivity, as well as an understanding of the microscopic conduction mechanism, ionic conduction pathways, and the role of the crystal structure in ionic conduction.