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Abstract Various researchers have studied fluctuations in pore‐scale phase occupancy during multiphase flow in porous media using synchrotron‐based X‐ray microcomputed tomography (micro‐CT). However, the impact of these fluctuations on the concept of a representative volume is not yet fully understood. In this study, we performed spatial and temporal averaging of multiphase flow experiments visualized with synchrotron‐based micro‐CT, focusing on oil saturation as the key parameter to determine a representative time‐and‐space average. Our findings revealed that a saturation value representative of both time and space was achieved during fractional flow experiments in drainage mode with fractional flows of 0.8, 0.5, and 0.3. Furthermore, we computed a range of relative permeabilities on the basis of whether momentaneous saturation or time‐and‐space averaged saturation was utilized for direct simulation. Our results highlighted the importance of time‐and‐space averaging in determining a representative relative permeability and indicated that the temporal and spatial scales covered in a typical micro‐CT flow experiment were sufficient to obtain a representative saturation value for sandstone rock under intermittent flow conditions. 

Abstract Sn‐based materials are identified as promising catalysts for the CO₂electroreduction (CO2RR) to formate (HCOO⁻). However, their insufficient selectivity and activity remain grand challenges. A new type of SnO₂nanosheet with simultaneous N dopants and oxygen vacancies (V_O‐rich N‐SnO₂NS) for promoting CO₂conversion to HCOO⁻is reported. Due to the likely synergistic effect of N dopant andV_O, theV_O‐rich N‐SnO₂NS exhibits high catalytic selectivity featured by an HCOO⁻Faradaic efficiency (FE) of 83% at−0.9 V and an FE of>90% for all C1 products (HCOO⁻and CO) at a wide potential range from −0.9 to−1.2 V. Low coordination Sn–N moieties are the active sites with optimal electronic and geometric structures regulated byV_Oand N dopants. Theoretical calculations elucidate that the reaction free energy of HCOO* protonation is decreased on theV_O‐rich N‐SnO₂NS, thus enhancing HCOO⁻selectivity. The weakened H* adsorption energy also inhibits the hydrogen evolution reaction, a dominant side reaction during the CO2RR. Furthermore, using the catalyst as the cathode, a spontaneous Galvanic Zn‐CO₂cell and a solar‐powered electrolysis process successfully demonstrated the efficient HCOO⁻generation through CO₂conversion and storage.