Nanocatalyst-Mediated Space Charge Orchestration to Enable Highly Efficient Interfacial Electron Transport in High-Temperature Electrochemical Devices.

High-temperature solid oxide electrochemical devices provide one of the most efficient, clean, and versatile platforms for hydrogen production and electric power generation. The formation of space charges at the interfaces within their multilayer structures has been intriguing, yet its nature remains poorly understood. Herein, we present an electrode design that enables precise space charge tailoring using regularly arrayed nanocatalysts. Our study demonstrates that a local electron-rich region develops within the space charge zone of a pure oxygen-ion conductor, gadolinia-doped ceria (GDC), at its interface with electronically conductive (Sm, Sr)CoO (SSC) nanocatalysts. We synthesized 20 nm-sized SSC nanocatalysts with well-defined geometries on a porous GDC scaffold using a highly controllable infiltration technique. When the interparticle distance decreased below a critical threshold, the local electron-rich regions overlapped, forming an extremely narrow yet continuous electron-conduction pathway throughout the ion-conducting matrix. This approach provides a well-balanced electronic and ionic conduction network along with a highly active surface enriched with nanocatalysts. Consequently, full cells incorporating this space-charge-mediated electrode exhibited remarkable performance and stability in both hydrogen and electricity production modes, significantly surpassing state-of-the-art counterparts that rely on bulk conduction pathways. Furthermore, this method was successfully scaled up for commercial-scale large cells, demonstrating the practical viability of space-charge engineering for real-world applications.