The surface electronic structures of catalysts need to be carefully engineered in CO2 reduction reaction (CO2RR), where the hydrogen evolution side reaction usually takes over under a significant overpotential, and thus dramatically lowers the reaction selectivity. Surface oxides can play a critical role in tuning the surface oxidation state of metal catalysts for a proper binding with CO2RR reaction intermediates, which may significantly improve the catalytic activity and selectivity. Here, we demonstrate the importance of surface-bonded oxygen on silver nanoparticles in altering the reaction pathways and improving the CO2RR performances. A comparative investigation on air-annealed Ag (Air-Ag) catalyst with or without the post-treatment of H2 thermal annealing (H2-Ag) was performed. In Air-Ag, the subsurface chemically bonded O species (O–Agδ+) was identified by angle resolved X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques, and contributed to the improved CO selectivity rather than H2in CO2RR electrolysis. As a result, though the maximal CO Faradaic efficiency of H2-Ag is at ∼30%, the Air-Ag catalyst presented a high CO selectivity of more than 90% under a current density of ∼21 mA/cm2.
Successful developments of new therapeutic strategies often rely on the ability to deliver exogenous molecules into cytosol. We have developed a versatile on-chip vortex-assisted electroporation system, engineered to conduct sequential intracellular delivery of multiple molecules into various cell types at low voltage in a dosage-controlled manner. Micro-patterned planar electrodes permit substantial reduction in operational voltages and seamless integration with an existing microfluidic technology. Equipped with real-time process visualization functionality, the system enables on-chip optimization of electroporation parameters for cells with varying properties. Moreover, the system’s dosage control and multi-molecular delivery capabilities facilitate intracellular delivery of various molecules as a single agent or in combination and its utility in biological research has been demonstrated by conducting RNA interference assays. We envision the system to be a powerful tool, aiding a wide range of applications, requiring single-cell level co-administrations of multiple molecules with controlled dosages.