Non-precious metal electrocatalysts (such as Fe–N–C materials) for the oxygen (O 2 ) reduction reaction demand a high catalyst loading in fuel cell devices to achieve workable performance. However, the extremely low solubility of O 2 in water creates severe mass transport resistance in the thick catalyst layer of Fe–N–C catalysts. Here, we introduce silicalite-1 nanocrystals with hydrophobic cavities as sustainable O 2 reservoirs to overcome the mass transport issue of Fe–N–C catalysts. The extra O 2 supply to the adjacent catalysts significantly alleviated the negative effects of the severe mass transport resistance. The hybrid catalyst (Fe–N–C@silicalite-1) achieved a higher limiting current density than Fe–N–C in the half-cell test. In the H 2 –O 2 and H 2 –air proton exchange membrane fuel cells, Fe–N–C@silicalite-1 exhibited a 16.3% and 20.2% increase in peak power density compared with Fe–N–C, respectively. The O 2 -concentrating additive provides an effective approach for improving the mass transport imposed by the low solubility of O 2 in water.
Zhongxi Xie,Shuang Liang,Xuechao Cai,Binbin Ding,Shanshan Huang,Zhiyao Hou,Ping’an Ma,Ziyong Cheng,Jun Lin
Hypoxia and overexpression of glutathione (GSH) are typical characteristics of the tumor microenvironment, which severely hinders cancer treatments. Here, we design a novel biodegradable therapeutic system, O2–Cu/ZIF-8@Ce6/ZIF-8@F127 (OCZCF), to simultaneously achieve GSH depletion and O2-enhanced combination therapy. Notably, the doped Cu2+ doubles the O2 storage capacity of the ZIF-8 matrix, which makes OCZCF an excellent pH-sensitive O2 reservoir for conquering tumor hypoxia, enhancing the photodynamic therapy (PDT) efficiency of chlorin e6 (Ce6) under 650 nm laser irradiation. Moreover, the released Cu2+ can act as a smart reactive oxygen species protector by consuming intracellular GSH. The byproduct Cu+ will undergo highly efficient Fenton-like reaction to achieve chemodynamic therapy (CDT) in the presence of abundant H2O2. The accompanying O2 will further alleviate hypoxia. The in vitro and in vivo experimental data indicate that OCZCF could cause remarkable tumor inhibition through enhanced synergetic PDT and CDT, which may open up a new path for cancer therapy.
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