Design and synthesis of oxygen reduction reaction (ORR) electrocatalysts with desired constituent based on understanding and exploitation of electrocatalytic mechanism is of great significance for applications of hydrochloride acid electrolysis. Herein, strongly coupled hybrid of watermelon-like RhxSy@C nanospheres has been rationally designed and synthesized via a one-step solvothermal method. X-ray photoelectron spectroscopy results reveal that the rhodium element presents in a mixture phase of metallic Rh and three sulfides, i.e., Rh17Sl5, Rh3S4 and Rh2S3. The ratio of the constituent phases, Rh/Rh17Sl5/Rh3S4/Rh2S3, is closely related to the synthesis parameter, and the average S/Rh molar ratio increases along with the increasing solvothermal temperature and duration. When assessed as electrocatalysts for ORR in hydrochloric acid, the RhxSy/C composite with a constituent of 29.1% Rh17S15, 45.8% Rh3S4 and 25.1% Rh2S3, where the ORR-active Rh17S15 and Rh3S4 phases are up to 75%, exhibits the best catalytic activity and stability, even outperforms Pt/C. In contrast, the metallic Rh-involved counterpart suffers from severe degradation in the highly corrosive environment, and the inactive Rh2S3 phase-dominant composite is less active toward ORR. Our results may give a new impetus to the rational design of rhodium sulfides with improved performance for hydrochloric acid electrolysis.

Rhodium sulfide/carbon nanocomposites were synthesized via a one-step alcohol-thermal method at 400 °C from Rh6(CO)16 and elemental S. Characterizations by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy revealed that the products were composed of amorphous carbon with spherical morphology and numerous highly crystallized Rh2S3/Rh17S15 nanocrystals, presented as uniform size composite nanospheres of 45–90 nm diameter. The crystallographic composition of rhodium sulfide in those composites depended on the initial S/Rh molar ratio and utilized solvent. Such hybrid nanomaterials displayed good dispersion of the rhodium sulfide nanoparticles, high surface area and extraordinary thermal/chemical resistance, making them attractive materials for electrocatalytic application of HCl electrolysis. Cyclic voltammetry and rotating disk electrode measurements were employed to evaluate the catalytic performance for oxygen reduction reaction in HCl electrolysis. It was illustrated that all rhodium sulfide/carbon nanocomposites were active towards oxygen reduction reaction. Especially, the catalyst synthesized in ethanol containing Rh17S15 phase outperformed commercial Pt/C in stability.

Highly ordered mesoporous carbon functionalized with carboxylate groups and magnetic nanoparticles has been successfully synthesized. By oxidative treatment using (NH4)2S2O8 and H2SO4 mixed solution, numerous hydrophilic groups were created in the mesopores without destroying the ordered mesostructure of CMK-3. Through the in situ reduction in Fe3+, magnetic nanoparticles were successfully introduced into the mesopores, resulting in the multifunctional mesoporous carbon Fe-CMK-3. The obtained hybrid carbon material possesses ordered mesostructure, high Brunauer–Emmett–Teller (BET) surface area up to 1013 m2/g, large pore volume of about 1.16 cm3/g, carboxylic surface, and excellent magnetic property. When used as an adsorbent, Fe-CMK-3 exhibits excellent performances for removing toxic organic compounds from waster-water, with a high adsorption capacity, an extremely rapid adsorption rate, and an easy magnetically separable process. In the case of requiring emergency removal of large amount of organic pollutants in aqueous, the hybrid carbon adsorbent would be an ideal choice.Graphical abstractHighlights► Ordered mesoporous carbon functionalized with carboxylate groups and magnetic nanoparticles. ► The functionalizations of mesoporous carbon material lead to an enhanced adsorption performance. ► Carboxylic functional groups result in an extremely rapid adsorption rate. ► Magnetic nanoparticles endow the mesoporous carbon with an easy magnetically separable process.

Rhodium sulfide/carbon nanocomposites were synthesized via a one-step alcohol-thermal method at 400 °C from Rh6(CO)16 and elemental S. Characterizations by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy revealed that the products were composed of amorphous carbon with spherical morphology and numerous highly crystallized Rh2S3/Rh17S15 nanocrystals, presented as uniform size composite nanospheres of 45–90 nm diameter. The crystallographic composition of rhodium sulfide in those composites depended on the initial S/Rh molar ratio and utilized solvent. Such hybrid nanomaterials displayed good dispersion of the rhodium sulfide nanoparticles, high surface area and extraordinary thermal/chemical resistance, making them attractive materials for electrocatalytic application of HCl electrolysis. Cyclic voltammetry and rotating disk electrode measurements were employed to evaluate the catalytic performance for oxygen reduction reaction in HCl electrolysis. It was illustrated that all rhodium sulfide/carbon nanocomposites were active towards oxygen reduction reaction. Especially, the catalyst synthesized in ethanol containing Rh17S15 phase outperformed commercial Pt/C in stability.