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With the rapid development of economy, the increasing energy crisis and environmental pollution urge us to develop sustainable and clean novel energy systems. Among them, the electrochemical energy conversion technology is considered as one of the ideal potential alternative energy systems, and the electrocatalysts play critical roles but are still challenging. Metal-organic frameworks (MOFs), thanks to their regular channels, atomically dispersed active centers, adjustable chemical and pore environments, have severed as promising electrocatalysts for electrochemical energy conversion. However, the relatively low conductivities and instabilities of MOFs limit their wide application in this field. In this case, fabricating hybrids of MOFs and carbon-based materials is an effective way to overcome above deficiencies. In addition, the synergistic effects between MOFs and carbons could optimize the electronic structures of active sites and promote the active surface areas, and thus improve the electrocatalytic performances of the composites. Herein, we outline the current development of MOF/carbon composites, including the fabrication methods of MOFs hybridized with various dimensions of carbon-based materials and the electrocatalysis utilization for water splitting, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and the oxygen reduction reaction (ORR). Finally, the advantages and challenges of such catalysts are highlighted and future endeavors on the development of MOF/carbon composites for the HER, OER and ORR are discussed.

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Adding a small amount of surfactant to a gas-liquid two-phase flow can markedly change the dynamic behavior of its bubbles. In this study, the lateral motion of a single bubble ( deq=1.99-3.33 mm, Reb=200-420) contaminated by surfactant and rising in a linear shear flow is experimentally studied. Sodium dodecyl sulfate (SDS) is chosen as the surfactant with concentrations ranging from 10 ppm to 50 ppm. A curved screen is used to generate a stable linear shear flow, and particle image velocimetry (PIV) is used to measure the quality of the flow field. Bubble motion parameters, including trajectory, aspect ratio, instantaneous velocity, terminal velocity, are captured using the shadow method with charge-coupled device (CCD) cameras. The lift coefficient CL is obtained by quasi-steady-state analysis. The results show that the presence of surfactant inhibits the lateral migration of bubbles rising in a shear flow and that increasing the SDS concentration and bubble equivalent diameter strengthens this inhibition effect. That is, the CL and the net lateral migration distance decreased with SDS concentration and bubble equivalent diameter. In addition, the variation trends of the quasi-steady drag coefficient, bubble terminal velocity, and bubble oscillation frequency with bubble equivalent diameter and SDS concentration also were analyzed.