Highly-efficient　oxygen　evolution　reaction　(OER)　and　reduction　of　carbon　dioxide　(CO2RR)　represent　the　two　biggest　scientific　challenges　in　artificial　photosynthesis.　Many　efficient　and　cost-affordable　electrocatalysts　have　been　reported　in　the　development　of　electrochemical　OER　and　CO2RR;　however,　during　the　electro-derived　oxidation　or　reduction　processes,　a　critical　fact　that,　most　catalysts　tend　to　undergo　structural　reconstruction　and/or　surface　rearrangement,　has　been　widely　observed,　which　greatly　subverts　the　traditional　conception　of　＇catalysts＇.　In　this　respect,　the　research　trends　have　gradually　transferred　from　optimizing　catalyst　materials　to　elucidating　the　real　active　sites　of　the　catalysts　as　well　as　understanding　the　underlying　mechanisms　behind　these　complex　reactions.　Most　importantly,　the　in　situ/operando　characterization　techniques　are　powerful　tools　to　achieve　this　goal.　Herein,　recent　advances　in　the　in　situ　X-ray　diffraction　and　absorption　spectroscopy　that　have　provided　a　unique　opportunity　to　investigate　the　structural　reconstruction　and/or　surface　rearrangement　of　catalysts　under　realistic　OER　and　CO2RR　conditions　are　thoroughly　reviewed.　Finally,　the　challenges　of　the　material　design　are　discussed,　and　the　future　perspective　for　developing　next-generation　catalysts　with　imperative　requirements　of　material　nature　is　provided.　This　journal　is　©　The　Royal　Society　of　Chemistry.