Robust High-performance Bifunctional Porous Cobalt MOF-Based Catalysts for Overall Water Splitting

MOF-based materials, as bifunctional catalysts for electrocatalytic water splitting, play an important role in the application and development of clean fuel hydrogen energy. This study presents a series of novel 3D Co-based MOFs with layered networks, including [Co(4,4'-bipy)0.5(aip)(CH3OH)·H2O]n (Co-MOF 1), [Co2(1,3'-bit)(aip)2(CH3OH)·H2O]n (Co-MOF 2), [Co(4,4'-bipb)(aip)]n (Co-MOF 3), and [Co2(4,4'-bipe)(aip)2·1.5H2O]n (Co-MOF 4). Their single-crystal structures of Co-MOFs 1-4 are characterized and analyzed before being applied in alkaline solutions for water decomposition (OER and HER). The electrocatalytic tests indicate that Co-MOFs 1-4 exhibit a good performance. Notably, Co-MOF 4 exhibits great behavior which has low overpotentials of 94 and 188 mV (OER) as well as 185 and 352 mV (HER) at the currents of 10 and 100 mA cm-2, respectively. In comparison with Co-MOFs 1-3, Co-MOF 4 has the lowest Tafel slopes, highest ECSA, and smallest resistance. The immanent qualities, such as distinct interwoven long chain layered structure, unsaturated coordination modes, and synergistic catalytic qualities among Co ions, contribute to explaining the results. The fundamentals provide valuable information for the investigation of innovative MOF-based bifunctional electrocatalysts for overall water splitting.

Homohelical Self-Assembly of Trimer of α-Cyclodextrin and Octamolybdate

The ability to conceptually mimic biomolecules to construct emergency-functional homospiral aggregates remains a long-standing challenge. Herein, we report artificial homohelical assembly by blending inorganic polyoxometalates (POMs) and organic cyclodextrin molecules. The chiral double-helical chains have been achieved by a left-hand arrangement of trimer-trimer. The trimer is formed by three {Mo8}@α-CD inclusive complexes as a Whittaker-style paddle wheel. During the process of assembly, chiral transfer and amplification from molecule to superstructure were observed. The enantioselective adsorption of the homohelical aggregate toward (R/S)-1,1'-binaphthyl-2,2'-diamine was further demonstrated. The interaction of {Mo8} and α-CD in solution was investigated. This work opens a wide scope for the design of a homohelix, enriching POM-based inorganic-organic materials.

Controlled assembly and reversible transformation of tuneable luminescent Mo8-R6G hybrids

This work reports that two new assemblies based on POM and AIE-quenched R6G display tuneable fluorescence intensity; furthermore two hybrids can be controllably synthesized and reversible transformation can also be achieved.

Dual-electrocatalysis behavior of star-like zinc-cobalt-sulfide decorated with cobalt-molybdenum-phosphide in hydrogen and oxygen evolution reactions

Although important advances have been acquired in the field of electrocatalysis, the design and fabrication of highly efficient and stable non-noble earth-abundant metal catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remain a significant challenge. In this study, we have designed a superior bifunctional catalyst for OER and HER in alkaline media based on the Co-Mo-P/Zn-Co-S multicomponent heterostructure. The as-prepared multicomponent heterostructure was successfully obtained via a simple three-step hydrothermal-sulfidation-electrodeposition process consisting of star-like Co-Zn-S covered with Co-Mo-P. The structure and morphology evaluation of the prepared catalysts were performed via Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, and elemental mapping techniques. The electrochemical tests show that Co-Mo-P/Co-Zn-S exhibits outstanding activity toward both OER and HER with OER overpotentials of 273 mV and 312 mV to drive the benchmark current densities of 10 and 50 mA cm^-2, respectively, with a Tafel slope of 41 mV dec^-1. In addition, the HER overpotentials of 120 mV and 165 mV were required to reach the benchmark current densities of 10 and 50 mA cm^-2, respectively, with a Tafel slope of 61.7 mV dec^-1 that outperforms most other state-of-the-art catalysts. In the case of HER, the prepared catalyst required an overpotential of 202 mV to reach the current density of 200 mA cm^-2 that was much lower than the overpotential of Pt/C (286 mV) to achieve the same current density. Co-Mo-P/Co-Zn-S also exhibits a suitable stability length of 10 h for OER and HER during the chronoamperometric tests. The superior performance of the Co-Mo-P/Co-Zn-S multicomponent heterostructure toward OER and HER may be related to the large specific surface area, accelerated mass and electron transport, and synergistic effect of multiple hybrid materials. These merits suggest that Co-Mo-P/Co-Zn-S can be considered as a promising catalyst for bi-functional OER and HER, and can be offered a great promise for future applications.