PNNL

Abstract

Protonic ceramic electrochemical cells (PCECs) have great potential to be a long-duration energy conversion and storage system. However, their operational stability has been severely limited under industrially relevant conditions (P_(H_2 O) = 40% and current density = 1 A cm-2). This degradation arises from the intrinsic chemical instability of doped barium cerate-based electrolytes and many oxygen electrode materials against H2O, and poor oxygen electrode–electrolyte interfacial contact. Here we present a conformally coated scaffold (CCS) structure design to comprehensively address these issues for the first time. Particularly, a porous proton-conducting scaffold is constructed and conformally coated with Pr1.8Ba0.2NiO4.1 (PBNO) electrocatalyst that has high chemical stability against H2O, triple conductivity, and hydration capability. This CCS design features strong PBNO–electrolyte interfacial bonding, thermomechanical stability, and an expanded proton conducting network, where PBNO conformal and protective layer can isolate various vulnerable electrolytes from H2O. We have verified the universality of this design with various proton-conducting electrolytes. This design strategy enables PCEC to reach a record-high 5000-hour electrolysis stability at -1.5 A cm-2 and 600 °C in 40% H2O with a voltage increase from 1.335 to 1.340 V and an average Faradaic efficiency of 70%, leading to an extremely low degradation rate of 1 µV h-1 (compared with 280–787 µV h-1 with durability for merely 100 h in other PCECs). Additionally, this design achieves exceptional fuel cell operation stability for 1000 h without any degradation (compared with tens to hundreds of µV h-1 in other PCECs). Integrated with H2 circulation and storage supporting components, a unitized regenerative PCEC (UR-PCEC) prototype system is demonstrated to stably operate under harsh long-duration deep cycling (12-hour interval to simulate the electricity storage and supply requirements in a day-night cycle) conditions without external H2 supply for 324 h. The CCS structure consolidates the electrode–electrolyte interfacial bonding to enable fast proton transfer in the percolated network with enhanced fluxes and kinetics, and protects the vulnerable electrolytes from H2O-induced decomposition. This work provides a general strategy to stabilize PCECs and offers new understanding and guidance for optimizing the electrode–electrolyte interfacial contact and ion transfer and enhancing the long-term stability with implications that could go beyond resilient and stable solid-state energy storage systems.