Structurally Engineered CNT-Confined MnxRu1-xO2 Catalysts for Efficient Acidic Oxygen Evolution at Low Ru Loading

Abstract

Developing acidic oxygen evolution reaction (OER) catalysts with low noble metal loading and high activity remains a critical challenge for advancing proton exchange membrane water electrolyzers. Herein, we report a structurally engineered MnxRu1-xO2 catalysts confined on carbon nanotubes (CNTs), enabling highly dispersed active sites and remarkable catalytic activity at low Ru content. The uniform nanoscale coating of MnxRu1-xO2 along CNT sidewalls promotes Mn-O-Ru interfacial bonding and establishes an electron-bridge for enhances charge transfer. The optimized CNT-(Mn0.75Ru0.25)O2 catalyst delivers an ultra-low overpotential of 120 mV at 10 mA cm⁻2 and an exceptional mass activity of 5549 A gRu-1 at 270 mV—252 times that of commercial RuO2 (22 A gRu-1). Combined X-ray spectroscopy, in-situ Raman, and differential electrochemical mass spectrometry reveal that the electron-rich Ru centers stabilized by Mn-O bridges accelerate charge transfer and suppress Ru dissolution during OER. Moreover, the CNT substrate and Ru incorporation synergistically generate abundant oxygen vacancies, significantly enhancing the catalytic activity through an improved lattice oxygen-mediated mechanism. This work highlights the critical role of CNT confinement and interfacial electronic modulation in decoupling noble metal usage from performance, offering a versatile design strategy for next-generation acidic OER catalysts.