This review article summarizes the progress of research on carbon nanomaterial-based lubricants witnessed in recent years. Carbon nanomaterials, such as graphene, carbon nanotubes (CNTs), fullerenes and carbon nanostructures, are at the center of current tribological research on attaining superior lubrication performance. The development of nanomaterial-based solid lubricants, lubricant additives and bulk materials and the related issues in their processing, characterization and applications as well as their tribological performance (coefficient of friction and wear rate) are listed in a structured tabulated form. Firstly, regarding nanomaterial-based solid lubricants, this study reveals that carbon nanomaterials such as graphite, graphene, graphene-based coatings and diamond-like carbon (DLC)-based coatings increase different tribological properties of solid lubricants. Secondly, this study summarizes the influence of graphene, carbon nanotubes, fullerene, carbon nanodiamonds, carbon nano-onions, carbon nanohorns and carbon spheres when they are used as an additive in lubricants. Thirdly, a structured tabulated overview is presented for the use of carbon nanomaterial-reinforced bulk material as lubricants, where graphene, carbon nanotubes and carbon nanodiamonds are used as reinforcement. Additionally, the lubricity mechanism and superlubricity of carbon nanomaterial-based lubricants is also discussed. The impact of carbon nanotubes and graphene on superlubricity is reviewed in detail. It is reported in the literature that graphene is the most prominent and widely used carbon nanomaterial in terms of all four regimes (solid lubricants, lubricating additives, bulk material reinforcement and superlubricity) for superior tribological properties. Furthermore, prospective challenges associated with lubricants based on carbon nanomaterials are identified along with future research directions.
With 65% rise in
the global demand, green hydrogen (H2) as a clean energy
carrier with high gravimetric energy density,
has emerged as a premier candidate in the past decade. The production
of sustainable and clean hydrogen through water electrolysis tends
to majorly rely on electrocatalysts with the scope of achieving exceptional
activity with low cost and excellent durability. The extensive use
of high cost noble metal HER electrocatalysts in the industry diverts
the attention to recent studies proposing that a proper design of
non-noble metal heterostructure could show comparable electrocatalytic
performance. Construction of interfaces appears as a solution to simultaneously
address multiple challenges and, at the same time, take advantage
of each component in constructing rich interfaces that could synergistically
enhance the HER activity in acidic, alkaline, and neutral environments.
This review describes the different forms of interfaces arising from
different heterostructures at the structural and atomic level, underlining
and correlating the principle mechanisms responsible for the performance
enhancement in the HER electrocatalysts. The first part of the review
recognizes the heterostructures at the micro/nano scale and at the
scale focusing mainly of 2D materials. Further, the interfaces at
the atomic level especially composed of chalcogenides, carbides, phosphides,
and nitrides are analyzed comprehensively based on their electrochemical
performance. Finally, the interfacial mechanisms arsing as a consequence
of the heterostructure formation are briefly described and correlated
to provide a better understanding in the future design of HER electrocatalysts.
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