Copper CO2 Reduction Electrocatalysts Studied by In-situ Soft X-ray Spectro-Ptychography

Abstract

A micro-chip based three-electrode electrochemical reactor enabling controlled, variable electrolyte flow, rapid electrolyte change and applied electrode potentials was used for in-situ soft X-ray spectro-ptychography of Cu particle catalysts under electrochemical CO2 reduction (CO2R) conditions. In comparison to scanning transmission X-ray microscopy (STXM), the spatial resolution was improved by a factor of three through measuring patterns of diffracted photons via spectro-ptychography. We present here a detailed study of how individual cubic Cu particles change morphology and oxidation state as a function of applied potential during CO2R. Quantitative chemical mapping by in-situ spectro-ptychography demonstrated that as-deposited, primarily mixed Cu(I) and Cu(0) particles were completely reduced to pure Cu(0) at an electrode potential of -0.2 VRHE, above the potential at which CO2R commences. At increasingly negative potentials, in the regime of CO2R, these Cu(0) particles underwent morphological changes, losing the initial cubic structure and forming irregular dendritic-like structures. This initial demonstration of in-situ soft X-ray spectro-ptychography sheds insight on the morphological and chemical structural changes of Cu particles in the CO2R regime and paves the way for more detailed in-situ studies of electrochemical materials and processes.

In Situ Studies of Copper-Based CO2 Reduction Electrocatalysts by Scanning Transmission Soft X-ray Microscopy

“…This has motivated us to pursue improving the spatial resolution of in situ soft X-ray spectro-microscopy by performing in situ spectro-ptychography, which provides similar chemical mapping to STXM but at ∼3 times better spatial resolution. 52,53 In our recent in situ spectro-ptychography study chemical changes and morphological evolution of a single ∼200 nm sized Cu catalyst particle were tracked from formation to CO 2 R conditions, demonstrating the ability to significantly improve upon the spatial resolution limits of STXM and advance in situ soft X-ray microscopy beyond the state-of-the-art measurements reported in the present work. 53…”

“…52,53 In our recent in situ spectro-ptychography study chemical changes and morphological evolution of a single ∼200 nm sized Cu catalyst particle were tracked from formation to CO 2 R conditions, demonstrating the ability to significantly improve upon the spatial resolution limits of STXM and advance in situ soft X-ray microscopy beyond the state-of-the-art measurements reported in the present work. 53…”

“…For example we recently demonstrated a 3-fold improvement in spatial resolution with similar chemical sensitivity to STXM and improved sensitivity to morphological changes, by performing in situ spectro-ptychography on this system using the same in situ device. 53…”

Operando methods: A new era of electrochemistry

“…Recently, operando resonant soft X-ray scattering (RSoXS) was developed to combine soft XAS studies of chemical environment and X-ray scattering of interparticle dynamics using a similar liquid-cell holder as EC-STEM [56]. Soft scanning transmission X-ray microscopy (STXM) was developed to provide nm-scale spatial resolution with simultaneous acquisition of an XAS spectrum [10,57]. Given an intense soft X-ray beam is focused into a nanoprobe, soft STXM has a high demand for sample stability in liquid under long-time beam exposure.…”