Nanoporous metals, a class of free-standing, high specific-area materials, evolve from interface-controlled self-organization in a selective dissolution (e.g., dealloying). The process creates randomly oriented pores, in which slow mass transport has limited the functional applications of nanoporous metals. Here the control of the pore orientation is demonstrated with a dealloying analogy, reduction-induced decomposition, achieved in flow cells. Via forced convection, the self-organization is placed under the control of sufficiently rapid mass transport to suppress pore branching and align 100 nm-wide ligaments and pores along the direction of reaction propagation, boosting the permeability by an order of magnitude while retaining the large surface area. The pore orientation can be further manipulated with a flow field for an orientation pattern akin to the expected fluid pattern, enabling a nanoporous silver electrode to deliver a peak power of 0.3 W cm