Zero-gap membrane electrode assembly (MEA) CO electrolyzer stands as a promising technology for circular carbon economy. However, current CO electrolyzers are energetically inefficient when operating at ampere-level current densities. Here, by analyzing the performance discrepancies between MEA and flow cells, we identify the depletion of K+ and water at the cathode as the main contributor to the low performance of MEA CO electrolyzers. This is attributed to the unique cathodic interface in catholyte-free MEA, where there is no aqueous electrolyte to maintain the three-phase interface. Through the development of needle-array catalysts with intensified electric fields (EFs) at their tips, we are able to concentrate the limited K+ cations onto the tips of the cathode, while simultaneously facilitating water uptake via electro-osmosis. We construct an MEA CO electrolyzer that achieves a large current density of 2,500 mA cm−2 at a voltage of only 2.7 V.