Synthesis of C/SiO2 nanoparticles
Preparation of HCS electrodes
Soaking of HCS and ALD/HCS electrodes
Electrochemical measurements
Materials characterizations
SiO2 sacrificial templates were removed with HF solution to achieve HCS. Typically, C/SiO2 nanoparticles were immersed in 10 wt % HF solution for different periods of time (see the Supplementary Materials), followed by centrifugation and ethanol washing three times. The SiO2 templates can be completely removed after 12 hours of etching. The final HCS were obtained after drying in a vacuum oven.