Duan et al. synthesized PtNi alloy nanowires at 450 °C and electrochemically dealloyed them to obtain jagged Pt nanowires; [9] and Zheng et al. prepared 1.1 nm Pt nanowires at 200 °C, with ethylenediamine chelated on the surface. [6a] In contrast to these ultrathin colloidal nanowires, Pt nanowire arrays (NWAs) are often synthesized with hard templates to guide the 1D growth. [10] The diameter of the resulting Pt nanowires usually exceeds 200 nm. [11] When applying colloidal nanowires as electrocatalysts, a loading process is a prerequisite. [1e,12] Thus, the Pt nanowires would inevitably stack together and the contact resistance among the nanowires becomes the bottleneck of electron transport. The addition of insulating binders like Nafion would further compromise the conductivity. [13] The packing of nanowires and polymers would also reduce the electrochemically active surface areas [13,14] and block diffusion paths. Hence, exploring new design of Pt electrocatalysts would be highly desirable but remains a significant challenge. Herein, we report a template-less method to directly grow arrays of ultrathin Pt nanowires on various substrate, a breakthrough given that Pt was previously incompatible with the method of Au nanowire arrays. [15] The surface of the Pt nanowires is covered with a layer of granular protrusions, the density of which could be readily tuned. On fluorinated tin oxide (FTO) substrate, such rough Pt NWAs exhibit enhanced electrocatalytic activity and stability toward the methanol oxidation reaction (MOR), with the highest mass activity of 1.24 A mg Pt −1 and specific activity of 35.71 mA cm −2 at 1.12 V (vs Ag/AgCl), which are 3.18 and 3.00 times higher than those of the commercial Pt/C catalysts. The Pt NWAs were grown directly from wafer substrate in solution. In a typical synthesis, Si wafer was first cleaned and treated with O 2 plasma to obtain surface hydroxyl groups and then immersed in a mixed solution containing 3-aminopropyltriethoxysilane (APTES) and acetic acid for 30 min to functionalize the surface with amine groups. After adsorbing 3-5 nm Pt nanoparticles [16] as seeds, the substrate was immersed in a water/ethanol (v/v = 1:1) reaction solution containing the ligand 2-mercapto-5-benzimidazolecarboxylic acid (MBIA, 110 × 10 −6 m), Pt precursor H 2 PtCl 6 (0.67 × 10 −3 m), and reductant NaBH 4 (3.33 × 10 −3 m). As the reaction was left undisturbed for the growth of nanowires, the bright finish of the substrate changed gradually to black, signifying Pt deposition. After 2 h, the substrate was retrieved, rinsed with water

Morphological coding of nanostructures represents a capability in rapid modulation of structural features and most importantly, the transcription of information into nanoscale. Exploiting the regioselectivity in the template-less electrochemical synthesis of ultrathin Au nanowires, we show that rapid alternation of applied potential would cause corresponding change in the width of the emerging nanowire segments. By understanding the growth kinetics, a strong correlation between the nanowire morphologies and the deposition potential is established and applied in emulating the Morse code.

Helical bundles that contain hundreds of ultrathin Au nanowires were synthesized in the solution phase via an unusual strain-induced curvature process.