Microfluidic fuel cells (MFCs) exploit the colaminar nature of aqueous electrolytes to separate the pair of electrodes, garnering tremendous interest as micropower devices. However, fuel crossover at high fuel concentrations prevents it from operating in practice. Here, a novel sequential-flow MFC is proposed with an air-breathing cathode placed upstream and a porous flow-through anode downstream. The electrolyte flows over the air-breathing cathode and then mixes with the fuel to flow through the porous anode. Benefitted from the fast electrolyte-convection rate, the sequential-flow MFC can effectively avoid fuel crossover. There is no obvious fuel-crossover phenomenon observed even on operating at 10 M fuel concentration. We discuss the impacts of electrode aspect ratios, spacing, fuel/electrolyte concentration, and volumetric flow rate/ ratio on the power-generation properties. It demonstrates that the electrodes with a low-aspect ratio configuration and narrow spacing can benefit the power output. A peak power density of 281 mW cm(-3) and a current density of 1433 mA cm(-3) are obtained in the sequential-flow MFC, surpassing those of the MFCs fed by formic acid- and formate fuels. These results demonstrate that the combinations of sequential flow with rational electrode arrangements and optimized operational conditions endow the MFCs with promising applications in powering chip-based analysis systems.