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The fast growth in human population and the quick cultural advancement of human society leads to the tremendous increase in energy demand. [1] During the past, fossil fuels were used as the main energy sources, while their excessive use based on the conventional combustion technology releases excessive greenhouse gases into the environment, causing adverse impact on the sustainability of ecosystem. To cope with the challenges of stringent environmental legislations and the reliance on fossil fuels, renewable Secondary Zn-air batteries (ZABs) are recognized as one of the most promising power sources for the future with lucrative features of low cost, high energy density, eco-friendliness, and high safety. However, the widespread implementation of ZABs is still hampered by the sluggish oxygen redox reactions. Thus the deployment of cost-effective and highly efficient air electrodes to substitute precious metals (Pt/Ir), is highly challenging, however, highly desired. Zeolitic imidazolate frameworks (ZIFs) are emerging functional materials, which demonstrate several outstanding characteristics, such as high specific surface area, high conductivity, self-doped N, open pore structure, versatile compositions and favourable chemical stability. Through varying the metal/organic moiety or by employing different synthesis protocols, ZIFs with different properties could be obtained. Being adaptable, desired functionalities may be further incorporated into ZIFs through pre-treatment, in situ treatment, and post treatment. Thus, ZIFs are the ideal precursors for the preparation of variety of bi-functional air electrodes for ZABs by materials tuning, morphological control, or by materials hybridization. Here, the recent advances of ZIFs-based materials are critically surveyed from the perspective of synthesis, morphology, structure and properties, and correlated with performance indicators of ZABs. Finally, the major challenges and future prospects of ZIFs associated with ZABs are discussed.

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The energy industry is exploring sustainable chemistry and engineering solutions for exploitation of shale reservoirs. Smectite-rich shale is challenging to drill with traditional water-based drilling fluid (WBDF). The objectives of this study are (i) to investigate acute toxicity of drilling fluids and (ii) to enhance the rheological properties, lubricity, and clay inhibition behavior of WBDF by adding Tween 80 (T80)/ZnO nanoparticles. Acute toxicity results revealed 100% survival rate of white leg shrimp in WBDF waste. At 0.7 g, the optimum concentration of T80ZnO, the plastic viscosity (PV) was improved by 12%; the negative surface charge of nanomaterial might have improved repulsion forces/stability and enhanced viscosity in the drilling fluids. Yield point (YP) was improved by 71%, moreover 10 min gel strength (GS) and 10 s GS were significantly increased by 32 and 54%, respectively. The metal oxide nanosolids induced heat transfer characteristics and ensured gelling and yield strength properties. Lubricity was slightly increased by 7%; the ZnO nanorods between the two sliding contact surfaces (i.e., assuming drill pipe and casing) improved lubricity. Filtrate loss (FL) volume was considerably minimized to 17 and 30% at API and high-pressure, high-temperature (HPHT) conditions, respectively; this observation could be explained by pores plugging in the filter paper. Heated clay swelling inhibition was optimized after addition of 0.6 g of T80ZnO nanoparticles to WBDF. The clay inhibition was enhanced by 9 and 17% when compared to conventional WBDF and fresh water, respectively; this progress might have attributed to the corresponding: (i) pores plugging in the clay and (ii) interparticle pores bridging between existing drilling additives and nanomaterial. The above findings identify that this drilling fluid could attain sustainable environmental and operational success while drilling into montmorillonite/smectite rich-clay and shale rock.

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The development of bi-functional electrocatalyst with high catalytic activity and stable performance for both oxygen evolution/reduction reactions (OER/ORR) in aqueous alkaline solution is key to realize practical application of zinc–air batteries (ZABs). In this study, we reported a new porous nano-micro-composite as a bi-functional electrocatalyst for ZABs, devised by the in situ growth of metal–organic framework (MOF) nanocrystals onto the micrometer-sized Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) perovskite oxide. Upon carbonization, MOF was converted to porous nitrogen-doped carbon nanocages and ultrafine cobalt oxides and CoN4 nanoparticles dispersing inside the carbon nanocages, which further anchored on the surface of BSCF oxide. We homogeneously dispersed BSCF perovskite particles in the surfactant; subsequently, ZIF-67 nanocrystals were grown onto the BSCF particles. In this way, leaching of metallic or organic species in MOFs and the aggregation of BSCF were effectively suppressed, thus maximizing the number of active sites for improving OER. The BSCF in turn acted as catalyst to promote the graphitization of carbon during pyrolysis, as well as to optimize the transition metal-to-carbon ratio, thus enhancing the ORR catalytic activity. A ZAB fabricated from such air electrode showed outstanding performance with a potential gap of only 0.83 V at 5 mA cm−2 for OER/ORR. Notably, no obvious performance degradation was observed for the continuous charge–discharge operation for 1800 cycles over an extended period of 300 h.