Many studies have accompanied the emergence of a great interest in flexible or/and stretchable devices for new applications in wearable and futuristic technology, including human-interface devices, robotic skin, and biometric devices, and in optoelectronic devices. Especially, new nanodimensional materials enable flexibility or stretchability to be brought based on their dimensionality. Here, the emerging field of flexible devices is briefly introduced using silver nanowires and graphene, which are famous nanomaterials for the use of transparent conductive electrodes, as examples, and their unique functions originating from the intrinsic property of these nanomaterials are highlighted. It is thought that this work will evoke more interest and idea exchanges in this emerging field and hopefully can trigger a breakthrough on a new type of optoelectronics and optogenetic devices in the near future.

Stretchable and/or flexible electrodes and their associated electronic devices have attracted great interest because of their possible applications in high-end technologies such as lightweight, large area, wearable, and biointegrated devices. In particular, metal nanowires and graphene derivatives are chosen for electrodes because they show low resistance and high mechanical stability. Here, we review stretchable and flexible soft electrodes by discussing in depth the intrinsic properties of metal NWs and graphenes that are driven by their dimensionality. We investigate these properties with respect to electronics, optics, and mechanics from a chemistry perspective and discuss currently unsolved issues, such as how to maintain high conductivity and simultaneous high mechanical stability. Possible applications of stretchable and/or flexible electrodes using these nanodimensional materials are summarized at the end of this review.

A major challenge in the development of electrocatalysts is to determine a detailed catalysis mechanism on a molecular level for enhancing catalytic activity. Here, we present bottom-up studies for an electrocatalytic hydrogen evolution reaction (HER) process through molecular activation to systematically control surface catalytic activity corresponding to an interfacial charge transfer in a porphyrin monolayer on inactive graphene. The two-dimensional (2D) assembly of porphyrins that create homogeneous active sites (e.g., electronegative tetrapyrroles (N)) on graphene showed structural stability against electrocatalytic reactions and enhanced charge transfer at the graphene-liquid interface. Performance operations of the graphene field effect transistor (FET) were an effective method to analyse the interfacial charge transfer process associated with information about the chemical nature of the catalytic components. Electronegative pristine porphyrin or Pt-porphyrin networks, where intermolecular hydrogen bonding functioned, showed larger interfacial charge transfers and higher HER performance than Ni-, or Zn-porphyrin. A process to create surface electronegativity by either central N or metal (M)-N played an important role in the electrocatalytic reaction. These findings will contribute to an in-depth understanding at the molecular level for the synergetic effects of molecular structures on the active sites of electrocatalysts toward HER.

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