Interaction between persistent free radicals (PFRs) and oxygen in biochar and its impact on gasification/combustion reactivity: An in-situ EPR study - Haotian Xu; Liqun Ma; Guangying Li; Dezhi Chen; Wei Deng; Kai Xu; Jun Xu; Long Jiang; Yi Wang; Sheng Su; Song Hu; Jun Xiang (Fuel, 2025)