On-line Inductively Coupled Plasma Mass Spectrometry Research Articles

Dynamic Activity and Stability of Transition Metal (oxy)Hydroxide Oxygen Evolution Electrocatalysts Under Steady and Intermittent Operation

The oxygen evolution reaction (OER) plays a critical role in several energy conversion technologies, requiring catalysts that combine high activity with stability for successful commercialization. Catalysts from first-row transition metal oxides have garnered considerable attention in this context. Their noteworthy OER activity and stability in alkaline environments position them as a more economical option than their counterparts in acidic media. However, recent studies have shown that these materials tend to experience significant dissolution issues and undergo changes in their chemical composition, a phenomenon observed even during steady-state operation.1–3 Addressing these challenges is essential for advancing commercial energy conversion technologies, which often face intermittent loads and reverse currents. A deeper understanding of the dynamic reconstruction under fluctuating conditions is crucial for developing more durable and efficient electrocatalytic materials.4 In this work, we investigate the dynamic performance of nickel cobalt (oxy)hydroxide electrocatalytic films containing iron active sites in alkaline media under steady and intermittent operation. First, we systematically examine the changes in OER catalytic activity in a typical three-electrode configuration, focusing on the incorporation and redissolution of iron and cerium during different electrochemical conditioning methods. As shown in Figure 1a, conditioning using chronopotentiometry decreases the OER overpotential without significantly shifting the redox peak. In contrast, conditioning using cyclic voltammetry significantly shifts the redox peak position (Figure 1b). These differences are attributed to the (oxy)hydroxide film thickness, which forms in situ during conditioning and affects the Fe dissolution and incorporation rates based on the conditioning method.5 We use different analytical techniques to probe chemical transformations during conditioning. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) are utilized to analyze compositional changes in the electrocatalytic films. Moreover, inductively coupled plasma mass spectrometry (ICP-MS) tracks metal dissolution.Next, we utilize an electrochemical flow electrolyzer with a zero-gap configuration, integrated with online ICP-MS and post-experimental TOF-SIMS and XPS, to study the reconstruction of these electrocatalysts under intermittent conditions. A NiFe anode operating in 6 M KOH with 1 ppm of Fe3+ shows a 40-mV change after 120 cycles of alternating low and high currents, including a simulated shutdown step (Figure 1c). This cell potential change, becoming more negative with continued cycling (Figure 1d), is attributed to the shutdown step. Our findings underscore how operating conditions affect the dynamic reconstruction of electrocatalytic materials, offering critical insights for developing more robust and resilient materials suitable for commercial applications.

Unraveling the role of introduced W in oxidation tolerance for Pt-based catalysts via on-line inductive coupled plasma-mass spectrometry

Water electrolysis cells and fuel cells have attracted considerable attention because they provide renewable and sustainable energy conversion and storage systems. Pt is the best catalyst for these two devices. However, cathodic Pt dissolution can occur after the oxidation of Pt, degrading the Pt catalyst. We report a PtW/C catalyst with high oxidation tolerance under repeated reverse-potential tests. The prepared PtW/C catalyst possesses higher oxidation tolerance than does the commercial Pt/C catalyst under repeated reverse-potential tests while showing comparable catalytic activity. From a combination of on-line inductively coupled plasma-mass spectrometry (ICP-MS) and ex-situ spectroscopy, we suggest that cathodic Pt dissolution is significantly inhibited because the introduced W suppresses the oxidation of Pt in PtW/C. However, W is dissolved in PtW/C rather than in Pt, indicating the need for further research. Our study demonstrates a new perspective for developing Pt-based catalysts with high oxidation tolerance by reducing cathodic Pt dissolution.

Electrocatalytic oxidation of 2-propanol on PtxIr100-x bifunctional electrocatalysts – A thin-film materials library study

Due to the high demand for renewable and infrastructure compatible energy conversion and storage technologies, research on organic fuel cells receives increasing interest again recently. Organic fuels such as alcohols provide an attractive avenue to overcome the drawbacks of hydrogen as an energy carrier. Particularly interesting are secondary alcohols that almost exclusively form ketones as the final oxidation product, as they can be utilized in “zero emission” concepts without CO2 as a by-product. The state-of-the-art electrocatalyst in secondary alcohol oxidation is Pt-Ru, which demonstrates low onset potentials for the oxidation of the most facile secondary alcohol isopropanol. Yet, the achievable current densities are still relatively low and decrease rapidly due to the formed product acetone, which can poison the catalyst surface over time. Therefore, there is an inevitable need for the development of novel electrocatalyst materials circumventing these challenges. In this study, we employ a high-throughput electrochemical approach coupled to on-line inductively-coupled plasma mass spectrometry to map the composition-dependent activity and stability of PtxIr100-x alloy electrocatalysts toward the electro-oxidation of isopropanol. The activity and stability of magnetron sputtered PtxIr100-x material libraries are studied in 0.1 M HClO4 both in the absence and presence of isopropanol. The highest current densities are achieved for the sample containing the least amount of Ir (3.4 at.%), with a continuous decrease with the increasing amount of Ir. The alloys are inactive towards the oxidation of isopropanol when the amount of Ir exceeded 80 at%. The presence of isopropanol also has a notable effect on stability: while dissolution rates do not change in the case of pure Pt and Ir, a significant increase in stability is observed for the PtxIr100-x thin-film samples at all applied upper potential limits. This is explained by the strong adsorption of acetone on the surface of the catalyst that inhibits the formation of surface oxides.

In-Operando Insights on the Hydrogen Evolution Reaction Activity and Stability of Non-Noble Metal Electrocatalysts for Water Electrolysis

Market penetration of proton exchange membrane water electrolysers (PEMWE) as energy conversion technologies in a renewable energy sector would imply, given the 2.3$/Kg H2 production cost aimed by the DoE,1 a drastic decrease in total noble metal electrocatalyst loading. For the state-of-the-art hydrogen evolution reaction (HER) catalyst, platinum, recent targets suggest this limit to be 0.05mgPt/cm2.2 In some applications, like direct photoelectrochemical water splitting, application of any amount of noble metal as a co-catalyst cannot be tolerated at all. Thus, given increasing scarcity of platinum, alternative materials based on earth-abundant non-noble metals represent a significant interest as promising HER catalysts. Among them, transition metal dichalcogenides such as molybdenum disulfide (MoS2) have provided excellent performances, particularly in their cluster-based allotropic structure [Mo3S13]2-.3 Whilst the role of sulfide atoms in the Mo-terminated edges as HER active sites in crystalline MoS2 is well-established, the HER mechanism of [Mo3S13]-based materials is still under debate. Preceded by an electrochemical activation step, operando spectroscopic studies ascribed the active sites to the electrochemically-cleaved S2 2-,4 but other reports have suggested undercoordinated Mo sites to be responsible for the HER activity.5 To date, no study has evaluated the in operando activity and stability of [Mo3S13]-based materials, shown to be intimately dependent on the electrochemical conditioning and electrolyte pH.6 This work devotes to the simultaneous detection of Mo and S species under HER operating conditions in pristine and anchored [Mo3S13]2- clusters to nitrogen-doped carbon nanotubes, by use of our dedicated on-line inductively-coupled plasma mass spectrometry (on-line ICP-MS). Our findings demonstrate, contrary to previous understanding, that the electrochemical activation step is mostly related to Mo dissolution rather than S loss, which is one order of magnitude lower. After such activation, Mo dissolution is significantly mitigated, whereas S dissolution is still observed, with magnitudes dependent on the anchoring material. The overarching picture obtained by such study enabled to shed light on the HER activation mechanism, and demonstrate that the stabilities of these materials are comparable to some Ir-based catalysts. The aforementioned results provide further guidelines to implement non-noble HER metal electrocatalysts in PEMWE.

In-Operando Insights on the Hydrogen Evolution Reaction Activity and Stability of Non-Noble Metal Electrocatalysts for Water Electrolysis

Market penetration of proton exchange membrane water electrolysers (PEMWE) as energy conversion technologies in a renewable energy sector would imply, given the 2.3$/Kg H2 production cost aimed by the DoE,1 a drastic decrease in total noble metal electrocatalyst loading. For the state-of-the-art hydrogen evolution reaction (HER) catalyst, platinum, recent targets suggest this limit to be 0.05mgPt/cm2.2 In some applications, like direct photoelectrochemical water splitting, application of any amount of noble metal as a co-catalyst cannot be tolerated at all. Thus, given increasing scarcity of platinum, alternative materials based on earth-abundant non-noble metals represent a significant interest as promising HER catalysts. Among them, transition metal dichalcogenides such as molybdenum disulfide (MoS2) have provided excellent performances, particularly in their cluster-based allotropic structure [Mo3S13]2-.3 Whilst the role of sulfide atoms in the Mo-terminated edges as HER active sites in crystalline MoS2 is well-established, the HER mechanism of [Mo3S13]-based materials is still under debate. Preceded by an electrochemical activation step, operando spectroscopic studies ascribed the active sites to the electrochemically-cleaved S2 2-,4 but other reports have suggested undercoordinated Mo sites to be responsible for the HER activity.5 To date, no study has evaluated the in operando activity and stability of [Mo3S13]-based materials, shown to be intimately dependent on the electrochemical conditioning and electrolyte pH.6 This work devotes to the simultaneous detection of Mo and S species under HER operating conditions in pristine and anchored [Mo3S13]2- clusters to nitrogen-doped carbon nanotubes, by use of our dedicated on-line inductively-coupled plasma mass spectrometry (on-line ICP-MS). Our findings demonstrate, contrary to previous understanding, that the electrochemical activation step is mostly related to Mo dissolution rather than S loss, which is one order of magnitude lower. After such activation, Mo dissolution is significantly mitigated, whereas S dissolution is still observed, with magnitudes dependent on the anchoring material. The overarching picture obtained by such study enabled to shed light on the HER activation mechanism, and demonstrate that the stabilities of these materials are comparable to some Ir-based catalysts. The aforementioned results provide further guidelines to implement non-noble HER metal electrocatalysts in PEMWE.

High Performance FeNC and Mn-oxide/FeNC Layers for AEMFC Cathodes

While the Anion Exchange Membrane Fuel Cell (AEMFC) is gaining interest due to high power performance recently achieved with platinum-group-metal (PGM) catalysts, its implementation will require high-performing PGM-free cathodes. FeNC catalysts have shown high activity and stability for the Oxygen Reduction Reaction (ORR) in alkaline electrolyte; however, the production of hydrogen peroxide during ORR can lead to premature degradation of FeNC and ionomer. In order to minimize the amount of peroxide formed on FeNC, α-MnO2, β-MnO2, δ-MnO2 and α-Mn2O3 were investigated as co-catalysts, with the aim of increasing the apparent activity of FeNC-based cathodes for the hydrogen peroxide reduction reaction (HPRR). The specific activity of α-Mn2O3 for the HPRR was distinctly superior to the other Mn-oxides. The four Mn-oxides were mixed with a FeNC catalyst comprising atomically-dispersed FeNx sites, showing higher HPRR activity and higher four-electron ORR selectivity than FeNC alone. The stability of α-Mn2O3/FeNC was studied operando by on-line inductively-coupled plasma mass spectrometry, to evaluate the potential and time dependent leaching of Mn and Fe. Finally, FeNC and α-Mn2O3/FeNC were applied at the cathode of AEMFCs, both achieving similar or higher current density at 0.9 V than a Pt/C commercial cathode, and peak power densities of ca. 1 W·cm−2.

(Invited) On-Line Inductively-Coupled Plasma Mass Spectrometry Characterization of Transition Metal Dissolution in Electrochemical Environments

While in-cell studies are the best way to characterize the performance and stability of electrochemical materials, the device environment often presents challenges to the real-time measurement of degradation processes. Several techniques have been developed to mimic the device environment, but to enable the real-time characterization of degradation processes. For example, low temperature fuel cell catalysts are often characterized using an aqueous electrolyte tuned to have pH and adsorption characteristics comparable to those of the solid ionomers used in fuel cells’ membrane-electrode assemblies. The material can then be subjected to various potential waveforms typical of those encountered in the device or intended to accelerate the materials degradation and the electrolyte analyzed, ex situ, for degradation products using a number of techniques. One such technique which is particularly useful is inductively-coupled mass spectrometry (ICP-MS), as it is able to detect transition metals in solution at concentrations as low at parts-per-trillion (ppt). This method, while valuable, provides limited information regarding the mechanisms of materials degradation (e.g., potential and time-dependence of dissolution processes). Recently, techniques have been developed which couple electrochemical flow or rotating disk electrode (RDE) cells directly to an ICP-MS allowing for precise time- and potential-resolved detection of dissolved species. One iteration of this technique is that pioneered by Mayrhofer et al. 1 in which a cell is sealed to a planar substrate on which the electrode material of interest is deposited. A stream of electrolyte is pumped over the material and the effluent electrolyte analyzed by ICP-MS. This cell can be rastered over the substrate/electrode material and thus has been dubbed a “scanning flow cell”. Lopes et al. 2 developed a stationary ICP-MS probe coupled with an RDE which allows measurement of the kinetics of a reaction simultaneously with detection of dissolution products. Another version of the technique uses a commercial flow cell from BASi with the electroactive material deposited on a glassy carbon working electrode and electrolyte drawn through the cell using the peristaltic pump of the ICP-MS.3,4 An overview of the application and utility of this technique in determining the potential-dependent degradation mechanisms of platinum and platinum alloy fuel cell catalysts will be presented. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Fuel Cell Performance and Durability Consortium (FC-PAD). Argonne National Laboratory is managed for the U.S. Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357. References O. Klemm, A. A. Topalov, C. A. Laska, K. J. J. Mayrhofer, Electrochem. Commun., 13, 1533 (2011).P. Lopes, D. Strmcnik, D. Tripkovic, J. G. Connell, V. Stamenkovic, and N.M. Markovic, Acs Catal, 6, 2536 (2016).P. Jovanovic, A. Pavlisic, V.S. Selih, M. Sala, N. Hodnik, M. Bele, S. Hocevar, and M. Gaberscek, Chemcatchem, 6, 449 (2014).R.K. Ahluwalia, D.D. Papadias, N.N. Kariuki, J.-K. Peng, X. Wang, Y. Tsai, D.G. Graczyk, and D.J. Myers, J. Electrochem. Soc., 165(6), F3024 (2018).

Quality control considerations for size exclusion chromatography with online ICP-MS: a powerful tool for evaluating the size dependence of metal-organic matter complexation.

Size exclusion chromatography (SEC), which separates molecules based on molecular volume, can be coupled with online inductively coupled plasma mass spectrometry (ICP-MS) to explore size-dependent metal-natural organic matter (NOM) complexation. To make effective use of this analytical dual detector system, the operator should be mindful of quality control measures. Al, Cr, Fe, Se, and Sn all exhibited columnless attenuation, which indicated unintended interactions with system components. Based on signal-to-noise ratio and peak reproducibility between duplicate analyses of environmental samples, consistent peak time and height were observed for Mg, Cl, Mn, Cu, Br, and Pb. Al, V, Fe, Co, Ni, Zn, Se, Cd, Sn, and Sb were less consistent overall, but produced consistent measurements in select samples. Ultrafiltering and centrifuging produced similar peak distributions, but glass fiber filtration produced more high molecular weight (MW) peaks. Storage in glass also produced more high MW peaks than did plastic bottles.