Depth-Profiling Microanalysis of CoNCN Water-Oxidation Catalyst Using a λ = 46.9 nm Plasma Laser for Nano-Ionization Mass Spectrometry

Abstract

Nanoscale depth profiling analysis of a CoNCN-coated electrode for water oxidation catalysis was carried out using table-top extreme ultraviolet (XUV) laser ablation time-of-flight mass spectrometry. The self-developed laser operates at λ = 46.9 nm and represents factor of 4 reduction in wavelength with respect to the 193 nm excimer laser. The reduction of the wavelength is an alternative approach to the reduction of the pulse duration, to enhance the ablation characteristics and obtain smaller quasi-nondestructive ablation pits. Such a XUV-laser ablation method allowed distinguishing different composite components of the catalyst-Nafion blend, used to modify a screen-printed carbon electrode surface. Chemical information was extracted by fragment assignment and relative amplitude analysis of the mass spectrometry peaks. Pure Nafion and the exposed carbon substrate were compared as references. Material specific fragments were clearly identified by the detected nonoverlapping mass-to-charge peaks of Nafion and CoNCN. Three dimensional mapping of relevant mass peak amplitudes was used to determine the lateral distribution and to generate depth profiles from consecutive laser pulses. Evaluating the profiles of pristine electrodes gave insight into fragmentation behavior of the catalyst in a functional ionomer matrix and comparison of post-catalytic electrodes revealed spots of thin localized Co residues.

XUV laser mass spectrometry for nano-scale 3D elemental profiling of functional thin films

“…State-of-the-art laser ablation has, however, a few limitations that may be addressed in the near future, thanks to shorter wavelengths [1,2]. First, the ablation mechanism is associated with thermo-mechanical processes that may modify the material composition, or damage a large portion of it.…”

“…Aim of this work was to compare the performance of traditional visible laser ablation microanalysis with more advanced short-wavelength (XUV) laser ablation, on the case of CZTS functional thin films for PV. Previous studies on water-oxidation catalysis showed a remarkable impact in mapping rapidly the 3D chemical and mechanical modifications of a sample cycled in the electrocatalytic system l [1]. The sample did not lose its functionality, such that it is in principle possible to deploy XUV-MS for real-time operando spectroscopy.…”

Tabletop extreme ultraviolet time‐of‐flight spectrometry for trace analysis of high ionization energy samples

“…Although agreement between the mass spectra acquired using the 26.5 eV and 10.5 eV lasers was highlighted, it was pointed out that the XUV ionization approach allows all the species in the sample to be measured, that are otherwise inaccessible with the 10.5 eV laser . Our own recent study showed the benefit of XUV depth profiling with TOF for nano‐scale microanalysis of water‐oxidation catalysts …”

Rapid quasi non-destructive 3D chemical visualization with tabletop x-ray laser mass spectrometry

“…The state-of-the-art short wavelength laser utilized for microanalysis has been for long time the excimer at 193nm [2][3][4][5][6][7] , with the spatial resolution in the large micron range. The cutting down of the laser wavelength is beneficial to (i) enhance the space resolution, (ii) eliminate elemental fractionation by using a high photon energy, (iii) improve the sample utilization efficiency, by efficient coupling as well as negligible plasma shielding.…”

“…A seminal paper by Kuznetsov et al 8 demonstrated the capability for nano-scale mass spectrometry (MS). Müller et al 3 showed that this implied a 5 orders of magnitude reduction of sampled mass, which did not turn into an equivalent reduction in MS sensitivity, thus concluding a more efficient sample utilization 9 . The occurrence of fractionation as well as matrix effects is expected to be mitigated compared to ion bombardement techniques, which demands further analysis.…”