ABSTRACT
Carbon material has widely been utilized in the synthesis of efficient carbon-supported Pt (Pt/C) catalysts, in which the structural properties greatly influence the electrocatalytic performances of Pt/C catalysts. However, the effects of intrinsic defects in carbon supports on the performance of the alkaline hydrogen evolution reaction (HER) have not been systematically investigated. Herein, porous carbon supports with different degrees of intrinsic defects were prepared by a simple template-assisted strategy, and the resulting samples were systematically studied by various analytical methods. The results suggested that the presence of abundant intrinsic defects (vacancy and topological defects) in the carbon support was advantageous in terms of favoring the dispersion and anchoring of Pt species, promoting electron transfer between Pt atoms and the carbon support, and tuning the electronic states of Pt species. These features improved the HER performance of Pt/C catalysts. Compared to the nontemplate-assisted carbon-supported Pt catalyst (Pt/NTC) with an overpotential of 178 mV, the optimized template-assisted carbon-supported Pt catalyst (Pt/TC) exhibited a lower overpotential of 58 mV at 10 mA cm-2. Besides, the Pt/TC catalyst displayed better HER durability than the Pt/NTC catalyst owing to its strong metal-support interaction. The DFT calculations confirmed the important role played by intrinsic defects (vacancy and topological defects) in stabilizing Pt atoms, with Pt-C3 coordination identified as the most favorable structure for improving the HER performance of Pt. Overall, novel insights on the significant contribution of intrinsic defects in porous carbon supports on the HER performances of Pt/C catalysts were provided, useful for future design and fabrication of advanced carbon-supported catalysts or other carbon-based electrode materials.
ABSTRACT
The oxygen functionalization of carbon materials has widely been employed to improve the catalytic performance of carbon-supported Pt (Pt/C) catalysts. Hydrochloric acid (HCl) has often been employed to clean carbons during the preparation of carbon materials. However, the effect of oxygen functionalization through a HCl treatment of porous carbon (PC) supports on the performance of the alkaline hydrogen evolution reaction (HER) has rarely been investigated. Herein, the impact of HCl combined with the heat treatment of PC supports on the HER performance of Pt/C catalysts has been comprehensively investigated. The structural characterizations revealed similar structures of pristine and modified PC. Nevertheless, the HCl treatment resulted in abundant hydroxyl and carboxyl groups and the further heat treatment formed thermally stable carbonyl and ether groups. Among the catalysts, Pt loading on the HCl-treated PC followed by a heat treatment at 700 °C (Pt/PC-H-700) exhibited elevated HER activity with a lower overpotential of 50 mV at 10 mA cm-2 when compared to the unmodified Pt/PC (89 mV). Pt/PC-H-700 also exhibited better durability than the Pt/PC. Overall, novel insights into the impact of the surface chemistry properties of porous carbon supports on the HER performance of Pt/C catalysts were provided, which were useful for highlighting the feasible improvement of HER performances by regulating the surface oxygen species of porous carbon supports.
ABSTRACT
Zinc-ion capacitors (ZICs) gain enormous attraction for their high power density, low cost, and long life, but their poor low-temperature performance is still a challenge due to the dissatisfactory freezing point of aqueous electrolyte solution. It is difficult for them to meet the requirements in cold environments as well as the extreme low temperature and severe temperature fluctuations in aerospace environments. Herein, ethanol (EtOH) solvent with ZnCl2 is used as an electrolyte to address these issues. Benefiting from the low freezing point (-114 °C) of EtOH, the ZIC with the ZnCl2/EtOH electrolyte can be operated at an ultralow temperature of -78 °C. It also demonstrates long cycling stability over 30,000 cycles. Such an enhancement is attributed to the unique properties of [ZnCl(EtOH)5]+ that can stabilize the coordination environment of Zn2+, slow the diffusivity, and raise the nucleation overpotential, leading to uniform Zn plating/stripping and subsequently suppressing dendrite growth. Meanwhile, the lower activation energy in ZnCl2/EtOH than that in ZnSO4/H2O electrolytes endows the ZIC excellent charge transfer properties. This work provides a fascinating electrolyte and a feasible pathway for ultra-low-temperature ZICs with a long cycling life.
