ELECTRODE, BATTERY CELL, CELL STACK, AND REDOX FLOW BATTERY SYSTEM

An electrode includes a carbon fiber, wherein the carbon fiber has a first region including a surface of the carbon fiber, when a cross section of the carbon fiber is analyzed by electron energy loss spectroscopy, the first region has peaks both around 285 eV and around 530 eV, and the first region is provided up to 10% of a diameter of the carbon fiber from the surface toward a center.