Redox-Tuned Ce-MOF Phosphides as Efficient Electrocatalysts for Anion Exchange Membrane Water Electrolysis

Abstract

Designing efficient and durable platinum-group-metal-free electrocatalysts is crucial for advancing anion-exchange membrane water electrolysis (AEMWE) toward practical green hydrogen production. Herein, we report a binder-free cerium-based metal−organic framework (Ce-MOF) electrode that is transformed into a porous phosphide-derived electrocatalyst through a simple phosphidation strategy while preserving the parent MOF architecture on nickel foam. The robust Ce−O coordination network formed between Ce ions and benzene-1,3,5-tricarboxylic acid (BTC) effectively maintains the structural integrity and hierarchical porosity of the framework during phosphidation, thereby retaining abundant accessible active sites. Meanwhile, the reversible Ce3+/Ce4+ redox couple acts as an intrinsic electron reservoir to promote charge transfer, whereas phosphorus incorporation simultaneously enhances electrical conductivity and tailors the local electronic structure, resulting in synergistically improved electrocatalytic activity. Consequently, the optimized Ce-BTC-P300 electrode exhibits outstanding bifunctional performance, requiring overpotentials of only 340 mV for the oxygen evolution reaction (OER) and 231 mV for the hydrogen evolution reaction (HER) to achieve an industrially relevant current density of 100 mA cm−1 in 1 M KOH. The electrode also demonstrates excellent durability, retaining more than 98% of its initial activity after 80 h for the OER and 100 h for the HER. When employed as both the anode and cathode in an AEMWE device, the catalyst delivers a high current density of 1 A cm−2 at a low cell voltage of 2.04 V under ambient conditions while maintaining stable long-term operation. This work establishes a rare-earth MOF-derived phosphidation strategy that integrates intrinsic redox buffering, robust structural stability, and enhanced electronic conductivity into a single catalyst platform, providing new insights into the rational design of high-performance, platinum-group-metal-free bifunctional electrocatalysts for practical alkaline water electrolysis.