Effect of Copper Deposit Morphology on the Characteristics of a Pt(Cu)/C-Catalyst Obtained by Galvanic Displacement

Polydisperse Pt Deposits Over TiO2-Nanotube-Array-Supported Ru Nanoparticles: Harnessing the Interfacial Synergy for Efficient Hydrogen Evolution Electrocatalysis

Developing cost-effective precious metal electrocatalysts for the hydrogen evolution reaction (HER) is key to realizing the economic viability of acidic water electrolysis. Herein, galvanic displacement is employed for in situ formation of bimetallic Pt/Ru deposits on H-intercalated TiO2 nanotube arrays. It is found that a two-step procedure yields polydisperse deposits with a dominant fraction of Ru nanoparticles coated with atomic and subnanometric Pt islands. These Pt|Ru nanointerfaces induce charge transfer from Pt to Ru, which modulates the electronic structure of Pt sites for accelerated HER kinetics. By varying the platinization time in the second step, a balance between the exposure of catalytically active Pt|Ru nanointerfaces and the total number of Pt surface sites is achieved. The optimized composite, termed Ru-30min@Pt-30min, requires an overpotential of 58 mV to deliver a current density of 100 mA cm-2 in 1.0 m HClO4 and maintains performance stability and structure integrity under prolonged operation. Moreover, it presents a 3.5-fold increase in precious metal mass activity over Pt/C at η = 80 mV. Theoretical calculations reveal that the electronic interactions generated by Pt-modification of Ru and hydrogenated TiO2 surfaces provide multiple active sites with improved Hads energetics compared to pure Pt and Ru.

Towards a full integration of vertically aligned silicon nanowires in MEMS using silane as a precursor

Silicon nanowires present outstanding properties for electronics, energy, and environmental monitoring applications. However, their integration into microelectromechanical systems (MEMS) is a major issue so far due to low compatibility with mainstream technology, which complicates patterning and controlled morphology. This work addresses the growth of 〈111〉 aligned silicon nanowire arrays fully integrated into standard MEMS processing by means of the chemical vapor deposition-vapor liquid solid method (CVD-VLS) using silane as a precursor. A reinterpretation of the galvanic displacement method is presented for selectively depositing gold nanoparticles of controlled size and shape. Moreover, a comprehensive analysis of the effects of synthesis temperature and pressure on the growth rate and alignment of nanowires is presented for the most common silicon precursor, i.e., silane. Compared with previously reported protocols, the redefined galvanic displacement together with a silane-based CVD-VLS growth methodology provides a more standard and low-temperature (<650 °C) synthesis scheme and a compatible route to reliably grow Si nanowires in MEMS for advanced applications.