Efficient propulsion of an electrocatalytic micromotor in a viscoelastic medium

Understanding how viscoelastic fluids influence the propulsion of catalytic Janus microswimmers is crucial for their application in targeted drug delivery and navigation through complex biofluids. We present a theoretical model of electrocatalytic self-propulsion of a bimetallic Janus microswimmer in a viscoelastic Oldroyd-B medium. The present model couples the charge conservation, ionic transport, the Michaelis–Menten surface reaction kinetics for hydrogen peroxide decomposition, and creeping-flow hydrodynamics, whereas the non-Newtonian viscoelastic rheology is captured using the Oldroyd-B model. The nonlinear governing equations are solved numerically using the finite element method. Results reveal swimming speed exhibits a non-monotonic dependence on fluid elasticity (quantified with the Deborah number De), with suppression at low values followed by recovery and saturation near De≈0.5. Increasing fuel concentration enhances ionic production, strengthens the self-generated electric field, and monotonically raises propulsion speed. A higher polymer concentration deepens the low-De velocity dip but increases the saturation speed at finite De. Reaction kinetics significantly modulate propulsion by altering surface charge asymmetry: stronger reduction kinetics enhance swimming, whereas increases in certain rate coefficients diminish it. We also report that viscoelasticity enhances the conversion efficiency, which quantifies the mechanical power extractable from a given chemical input. Viscoelasticity can improve electrocatalytic performance by up to threefold relative to Newtonian media. These findings underscore the critical interplay between surface reaction kinetics and fluid viscoelasticity in controlling micromotor propulsion, indicating that optimizing electrical parameters and fluid properties can significantly improve performance.