Elucidating Cathodic Corrosion Mechanisms with Operando Electrochemical Transmission Electron Microscopy

Abstract

Cathodic corrosion represents an enigmatic electrochemical process in which metallic electrodes corrode under sufficiently reducing potentials. Although discovered by Fritz Haber in the 19th century, only recently has progress been made in beginning to understand the atomistic mechanisms of corroding bulk electrodes. The creation of nanoparticles as the end-product of the corrosion process suggests an additional length scale of complexity. Here, we studied the dynamic evolution of morphology, composition, and crystallographic structural information of nanocrystal corrosion products by analytical and fourdimensional electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM). Our operando/in situ electron microscopy revealed, in real-time, at the nanometer scale, that cathodic corrosion yields significantly higher levels of structural degradation for heterogeneous nanocrystals than bulk electrodes. In particular, the cathodic corrosion of Au nanocubes on bulk Pt electrodes led to the unexpected formation of thermodynamically immiscible Au−Pt alloy nanoparticles. The highly kinetically driven corrosion process is evidenced by the successive anisotropic transition from stable Pt(111) bulk single-crystal surfaces evolving to energetically less-stable (100) and ( 110) steps. The motifs identified in this microscopy study of cathodic corrosion of nanocrystals are likely to underlie the structural evolution of nanoscale electrocatalysts during many electrochemical reactions under highly reducing potentials, such as CO 2 and N 2 reduction.

The New Era of High-Throughput Nanoelectrochemistry

“…456,457 Even stronger reductive potentials are accompanied by considerable reconstruction and corrosion of metallic nanostructures. LC-TEM was used to track such cathodic-corrosion phenomenon during HER at the more stable Pt(111) surface 449,458 to the more reactive system of single Au nanocubes deposited on Pt bulk. 449 Both morphological and compositional changes of the Au nanostructures and of the Pt support were evidenced.…”

The new era of high throughput nanoelectrochemistry

“…440,449 Its advantage is the possibility to perform multiple characterizations (Figure 16A). In addition to the operando imaging, developments to improve imaging in situ include the growth of a gas bubble to limit the liquid thickness and improve the resolution, 450 or postmortem or ex situ (after removal of the liquid) analysis at the same location to enable, inter alia: better resolution of morphology, detection of crystal structures by electron diffraction, to allow the analysis of deformation in nanocrystals, and chemical identification by X-ray spectroscopy. A significant focus has been towards the operando evaluation of the durability of materials under electrochemical conditions.…”

“…457,458 Even stronger reductive potentials are accompanied by considerable reconstruction and corrosion of metallic nanostructures. LC-TEM was used to track such cathodic-corrosion phenomenon during HER at the more stable Pt(111) surface 450,459 to the more reactive system of single Au nanocubes deposited on Pt bulk. 450 Both morphological and compositional changes of the Au nanostructures and of the Pt support were evidenced.…”

“…LC-TEM was used to track such cathodic-corrosion phenomenon during HER at the more stable Pt(111) surface 450,459 to the more reactive system of single Au nanocubes deposited on Pt bulk. 450 Both morphological and compositional changes of the Au nanostructures and of the Pt support were evidenced. The strategy presented in Figure 16A to improve the resolution enables complementary in situ and postmortem imaging insights of this process with nm to the atomic scale resolution (Figure 16D).…”

“…particularly evidences the formation of Au-Pt alloys during the corrosion process, likely through metal hydride formation 450. …”