  Spontaneous imbibition enables the elegant propelling of nano-flows because
of the dominance of capillarity at small length scales. The imbibition kinetics
are, however, solely determined by the static geometry of the porous host, the
capillarity, and the fluidity of the imbibed liquid. This makes active control
particularly challenging. Here, we show for aqueous electrolyte imbibition in
nanoporous gold that the fluid flow can be reversibly switched on and off
through electric potential control of the solid-liquid interfacial tension,
i.e. we can accelerate the imbibition front, stop it, and have it proceed at
will. Simultaneous measurements of the mass flux and the electrical current
allow us to document simple scaling laws for the imbibition kinetics, and to
explore the charge flow dynamics in the metallic nanopores. Our findings
demonstrate that the high electric conductivity along with the pathways for
ionic and/or fluid transport render nanoporous elemental gold a versatile,
accurately controllable electro-capillary pump and flow sensor for minute
amounts of liquids with exceptionally low operating voltages.
