Electrochemical reduction of carbon dioxide (CO) to carbon monoxide (CO) is the first step in the synthesis of more complex carbon-based fuels and feedstocks using renewable electricity. Unfortunately, the reaction suffers from slow kinetics owing to the low local concentration of CO surrounding typical CO reduction reaction catalysts. Alkali metal cations are known to overcome this limitation through non-covalent interactions with adsorbed reagent species, but the effect is restricted by the solubility of relevant salts. Large applied electrode potentials can also enhance CO adsorption, but this comes at the cost of increased hydrogen (H) evolution. Here we report that nanostructured electrodes produce, at low applied overpotentials, local high electric fields that concentrate electrolyte cations, which in turn leads to a high local concentration of CO close to the active CO reduction reaction surface. Simulations reveal tenfold higher electric fields associated with metallic nanometre-sized tips compared to quasi-planar electrode regions, and measurements using gold nanoneedles confirm a field-induced reagent concentration that enables the CO reduction reaction to proceed with a geometric current density for CO of 22 milliamperes per square centimetre at -0.35 volts (overpotential of 0.24 volts). This performance surpasses by an order of magnitude the performance of the best gold nanorods, nanoparticles and oxide-derived noble metal catalysts. Similarly designed palladium nanoneedle electrocatalysts produce formate with a Faradaic efficiency of more than 90 per cent and an unprecedented geometric current density for formate of 10 milliamperes per square centimetre at -0.2 volts, demonstrating the wider applicability of the field-induced reagent concentration concept.

We have studied friction and dissipation in single and bilayer graphene films grown epitaxially on SiC. The friction on SiC is greatly reduced by a single layer of graphene and reduced by another factor of 2 on bilayer graphene. The friction contrast between single and bilayer graphene arises from a dramatic difference in electron-phonon coupling, which we discovered by means of angle-resolved photoemission spectroscopy. Bilayer graphene as a lubricant outperforms even graphite due to reduced adhesion.

E. H. (2022). Quantum-size-tuned heterostructures enable efficient and stable inverted perovskite solar cells. Nature Photonics.

The superior mechanical behavior of carbon nanotubes (CNT) and their electrical and thermal functionalities has motivated researchers to exploit them as building blocks to develop advanced materials. Here, we demonstrate high performance double-walled nanotube (DWNT)-polymer composite yarns formed by twisting and stretching of ribbons of randomly oriented bundles of DWNTs thinly coated with polymeric organic compounds. A multiscale in situ scanning electron microscopy experimental approach was implemented to investigate the mechanical performance of yarns and isolated DWNT bundles with and without polymer coatings. DWNT-polymer yarns exhibited significant ductility of ∼20%, with energy-to-failure of as high as ∼100 J g(-1), superior to previously reported CNT-based yarns. The enhanced ductility is not at the expense of strength, as yarns exhibited strength as high as ∼1.4 GPa. In addition, the significance of twisting on the densification of yarns and corresponding enhancement in the lateral interactions between bundles is identified. Experiments at nanometer and macroscopic length scales on DWNT-polymer yarns and bundles further enabled quantification of energy dissipation/storage mechanisms in the yarns during axial deformations. We demonstrate that while isolated DWNT bundles are capable of storing/dissipating up to ∼500 J g(-1) at failure, unoptimal load transfer between individual bundles prevents the stress build up in the yarns required for considerable energy storage at the bundle level. By contrast, through polymer lateral interactions, a much better performance is obtained with the majority of energy dissipated at failure being contributed by the interactions between the polymer coating and the DWNTs as compared to the direct van der Waals interactions between bundles.

The work function difference between single layer and bilayer graphene grown epitaxially on 6H-SiC(0001) has been determined to be 135±9 meV by means of the Kelvin probe force microscopy. Bilayer films are found to increase the work function as compared to single layer films. This method allows an unambiguous distinction between interface layer, single layer, and bilayer graphene. In combination with high-resolution topographic imaging, the complex step structure of epitaxial graphene on SiC can be resolved with respect to substrate and graphene layer steps.

E. H. (2022). Regulating surface potential maximizes voltage in all-perovskite tandems. Nature.

A unique size-dependent strain hardening mechanism, that achieves both high strength and ductility, is demonstrated for penta-twinned Ag nanowires (NWs) through a combined experimental-computational approach. Thin Ag NWs are found to deform via the surface nucleation of stacking fault decahedrons (SFDs) in multiple plastic zones distributed along the NW. Twin boundaries lead to the formation of SFD chains that locally harden the NW and promote subsequent nucleation of SFDs at other locations. Due to surface undulations, chain reactions of SFD arrays are activated at stress concentrations and terminated as local stress decreases, revealing insensitivity to defects imparted by the twin structures. Thick NWs exhibit lower flow stress and number of distributed plastic zones due to the onset of necking accompanied by more complex dislocation structures.

Electron irradiation induced covalent cross‐linking at multiple length scales within double‐walled nanotube bundles is demonstrated to lead to ultrahigh effective strength and stiffness. In situ transmission electron microscopy tensile testing reveals both order of magnitude enhancements in the mechanical properties as well as distinct failure mechanisms of cross‐linked versus un‐crosslinked bundles.