Spectro Inlets

Allotrope-dependent activity-stability relationships of molybdenum sulfide hydrogen evolution electrocatalysts

DAY01 — Mon, 29 Apr 2024 10:00:29 +0000

Molybdenum disulfide (MoS₂) is widely regarded as a competitive hydrogen evolution reaction (HER) catalyst to replace platinum in proton exchange membrane water electrolysers (PEMWEs). Despite the extensive knowledge of its HER activity, stability insights under HER operation are scarce. This is paramount to ensure long-term operation of Pt-free PEMWEs, and gain full understanding on the electrocatalytically-induced processes responsible for HER active site generation.

The latter are highly dependent on the MoS₂ allotropic phase, and still under debate. We rigorously assess these by simultaneously monitoring Mo and S dissolution products using a dedicated scanning flow cell coupled with downstream analytics (ICP-MS), besides an electrochemical mass spectrometry setup for volatile species analysis. We observe that MoS₂ stability is allotrope-dependent: lamellar-like MoS₂ is highly unstable under open circuit conditions, whereas cluster-like amorphous MoS_3-x instability is induced by a severe S loss during the HER and undercoordinated Mo site generation. Guidelines to operate non-noble PEMWEs are therefore provided based on the stability number metrics, and an HER mechanism which accounts for Mo and S dissolution pathways is proposed.

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Real-Time Detection of Acetaldehyde in Electrochemical CO Reduction on Cu Single Crystal

DAY01 — Mon, 12 Feb 2024 10:00:29 +0000

Aqueous zinc metal batteries (AZMB) are emerging as a promising alternative to the prevailing existing Lithium-ion battery technology. However, the development of AZMBs is hindered due to challenges including dendrite formation, hydrogen evolution reaction (HER), and ZnO passivation on the anode. Here, a tetraalkylsulfonamide (TAS) additive for suppressing HER, dendrite formation, and enhancing cyclability is rationally designed. Only 1 mm TAS is found that can effectively displace water molecules from the Zn²⁺ solvation shell, thereby altering the solvation matrix of Zn²⁺ and disrupting the hydrogen bond network of free water, as demonstrated through ⁶⁷ Zn and ¹H nuclear magnetic resonance spectroscopy, high-resolution mass spectrometry (HRMS), and density functional theory (DFT) studies. Voltammetry synchronized with in situ monitoring of the electrode surface reveals suppressed dendritic growth and HER in the presence of TAS. Electrochemical mass spectrometry (ECMS) captures real-time HER suppression during Zn electrodeposition, revealing the ability of TAS to suppress the HER by an order of magnitude. A ≈25-fold cycle life improvement from ≈100 h to over 2500 h in coin cells cycled in the presence of TAS. Furthermore, by suppressing passivation product formation, it is demonstrated that strategy robustly maximizes the stability of Zn metal anodes.

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How Solvation Energetics Dampen the Hydrogen Evolution Reaction to Maximize Zinc Anode Stability

DAY01 — Mon, 12 Feb 2024 10:00:29 +0000

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Gold Nanoparticles for CO2 Electroreduction: An Optimum Defined by Size and Shape

DAY01 — Tue, 09 Jan 2024 10:00:29 +0000

Understanding the size-dependent behavior of nanoparticles is crucial for optimizing catalytic performance. We investigate the differences in selectivity of size-selected gold nanoparticles for CO₂ electroreduction with sizes ranging from 1.5 to 6.5 nm. Our findings reveal an optimal size of approximately 3 nm that maximizes selectivity toward CO, exhibiting up to 60% Faradaic efficiency at low potentials. High-resolution transmission electron microscopy reveals different shapes for the particles and suggests that multiply twinned nanoparticles are favorable for CO₂ reduction to CO. Our analysis shows that twin boundaries pin 8-fold coordinated surface sites and in turn suggests that a variation of size and shape to optimize the abundance of 8-fold coordinated sites is a viable path for optimizing the CO₂ electrocatalytic reduction to CO. This work contributes to the advancement of nanocatalyst design for achieving tunable selectivity for CO₂ conversion into valuable products.

This publication is licensed under CC-BY-NC-ND 4.0

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For Zinc Metal Batteries, How Many Electrons go to Hydrogen Evolution? An Electrochemical Mass Spectrometry Study

DAY01 — Tue, 02 Jan 2024 10:00:29 +0000

Despite the advantages of aqueous zinc (Zn) metal batteries (AZMB) like high specific capacity (820 mAh g⁻¹ and 5,854 mAh cm⁻³), low redox potential (−0.76 V vs. the standard hydrogen electrode), low cost, water compatibility, and safety, the development of practically relevant batteries is plagued by several issues like unwanted hydrogen evolution reaction (HER), corrosion of Zn substrate (insulating ZnO, Zn(OH)₂, Zn(SO₄)_x(OH)_y, Zn(ClO₄)_x(OH)_y etc. passivation layer), and dendrite growth. Controlling and suppressing HER activity strongly correlates with the long-term cyclability of AZMBs.

Therefore, a precise quantitative technique is needed to monitor the real-time dynamics of hydrogen evolution during Zn electrodeposition. In this study, we quantify hydrogen evolution using in situ electrochemical mass spectrometry (ECMS). This methodology enables us to determine a correction factor for the faradaic efficiency of this system with unmatched precision. For instance, during the electrodeposition of zinc on a copper substrate at a current density of 1.5 mA/cm² for 600 seconds, 0.3 % of the total charge is attributed to HER, while the rest contributes to zinc electrodeposition. At first glance, this may seem like a small fraction, but it can be detrimental to the long-term cycling performance of AZMBs. Furthermore, our results provide insights into the correlation between HER and the porous morphology of the electrodeposited zinc, unravelling the presence of trapped H₂ and Zn corrosion during the charging process. Overall, this study sets a platform to accurately determine the faradaic efficiency of Zn electrodeposition and provides a powerful tool for evaluating electrolyte additives, salts, and electrode modifications aimed at enhancing long-term stability and suppressing the HER in aqueous Zn batteries.

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Probing Degradation in Lithium Ion Batteries with On-Chip Electrochemistry Mass Spectrometry

DAY01 — Sat, 16 Dec 2023 10:00:29 +0000

The rapid uptake of lithium ion batteries (LIBs) for large scale electric vehicle and energy storage applications requires a deeper understanding of the degradation mechanisms. Capacity fade is due to the complex interplay between phase transitions, electrolyte decomposition and transition metal dissolution; many of these poorly understood parasitic reactions evolve gases as a side product. Here we present an on-chip electrochemistry mass spectrometry method that enables ultra-sensitive, fully quantified and time resolved detection of volatile species evolving from an operating LIB. The technique’s electrochemical performance and mass transport is described by a finite element model and then experimentally used to demonstrate the variety of new insights into LIB performance. We show the versatility of the technique, including (a) observation of oxygen evolving from a LiNiMnCoO₂ cathode and (b) the solid electrolyte interphase formation reaction on graphite in a variety of electrolytes, enabling the deconvolution of lithium inventory loss (c) the first direct evidence, by virtue of the improved time resolution of our technique, that carbon dioxide reduction to ethylene takes place in a lithium ion battery. The emerging insight will guide and validate battery lifetime models, as well as inform the design of longer lasting batteries.

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Correlating oxygen functionalities and electrochemical durability of carbon supports for electrocatalysts

DAY01 — Sat, 25 Nov 2023 10:00:29 +0000

Achieving high durability of the polymer electrolyte membrane (PEM) fuel cell catalysts remains a major challenge. While most of the research focuses on the active phase, carbon support remains overlooked. In this study durability of carbon support materials for Pt alloy nanoparticles is critically evaluated. First graphene derivative (GD) based carbon supports with different chemical properties are prepared and utilized along with widely used commercial carbon black (CB) material. High-temperature electrochemical accelerated degradation tests (HT-ADTs) combined with X-ray photoelectron spectroscopy (XPS) show that the total amount of oxygen functionalities, the type of oxygen functionalities, and sp² carbon content play a crucial role in carbon support durability. The observations were confirmed with the direct online measurements of carbon corrosion via an advanced in-situ technique – an electrochemical cell coupled with a mass spectrometer (EC-MS). We report that increasing the content of sp² carbon and decreasing carboxyl functional groups have the most beneficial effect on stability. The study provides important guidelines for tailoring the carbon support properties and their relationship to the durability of the electrocatalyst, which could be crucial for producing more stable catalysts and achieving the Department of Energy’s fuel cell system lifetime targets. Moreover, the innovative carbon design approach presented here could be applied in other fields such as batteries, supercapacitors, sensors and others.

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Searching for the Rules of Electrochemical Nitrogen Fixation

DAY01 — Thu, 02 Nov 2023 10:00:29 +0000

Li-mediated ammonia synthesis is, thus far, the only electrochemical method for heterogeneous decentralized ammonia production. The unique selectivity of the solid electrode provides an alternative to one of the largest heterogeneous thermal catalytic processes. However, it is burdened with intrinsic energy losses, operating at a Li plating potential. In this work, we survey the periodic table to understand the fundamental features that make Li stand out. Through density functional theory calculations and experimentation on chemistries analogous to lithium (e.g., Na, Mg, Ca), we find that lithium is unique in several ways. It combines a stable nitride that readily decomposes to ammonia with an ideal solid electrolyte interphase, balancing reagents at the reactive interface. We propose descriptors based on simulated formation and binding energies of key intermediates and further on hard and soft acids and bases (HSAB principle) to generalize such features. The survey will help the community toward electrochemical systems beyond Li for nitrogen fixation.

This publication is licensed under CC-BY 4.0 .

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Determining the potential-dependent identity of methane adsorbates at Pt electrodes using EC-MS

DAY01 — Mon, 23 Oct 2023 10:00:29 +0000

The increased availability of methane resulting from shale gas extraction and renewable feedstocks has made the development of technologies that can utilize this resource in a distributed setting a valuable target. Methane can be leveraged as a resource through its electrochemical partial oxidation to more valuable liquid chemicals, such as methanol, and its total oxidation to generate electricity. Enabling the partial and total oxidation of methane requires an understanding of the surface chemistry of methane under applied potentials. Herein we employ electrochemical mass spectrometry (EC-MS) to investigate the potential-dependent distribution of surface compounds generated from adsorbed methane under ambient conditions. By directly measuring the products of adsorbate oxidation using EC-MS we found that methane adsorption has a strong potential dependence with maximum adsorption at 0.3 V vs. RHE, and *CO is the dominant surface intermediate independent of the potential at which methane is adsorbed. Our findings explain why Pt is a poor catalyst for the electrocatalytic partial oxidation of methane and point the way to better catalyst materials for electrocatalytically valorizing methane in chemical synthesis and electricity generation.

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Benchmarking Electrocatalyst Stability for Acidic Oxygen Evolution Reaction: The Crucial Role of Dissolved Ion Concentration

DAY01 — Thu, 19 Oct 2023 10:00:29 +0000

Developing robust catalysts for the acidic oxygen evolution reaction (OER) is critical for large-scale implementation of proton exchange membrane (PEM) water electrolyzers. A promising strategy is to stabilize Ru-based catalysts by suppressing Ru dissolution, which requires knowledge of RuO₂ stability. This work explores the influences on measuring the stability number of RuO₂ and presents a comprehensive analysis and comparison of its stability with other electrocatalysts. We observe that RuO₂ shows relatively higher stability in electrolytes with a confined working volume because of the Nernst shift caused by the concentration buildup of dissolved Ru. The stability number of RuO₂ has a negligible dependence on the measurement duration, applied current density, Nafion content, and substrate materials. Furthermore, we analyze the effects of these factors on other typical OER catalysts and identify that the concentration of dissolved ions is key to understanding the stability number measured by different electrochemical cells and the claimed excellent stability of non-noble catalysts reported in the literature. In addition, the comparison of the stability number and intrinsic activity of RuO₂, IrO₂, and non-noble catalysts demonstrates that RuO₂ is at least 2 orders of magnitude less stable but also 10-fold more active than IrO₂ and that noble catalysts significantly outperform non-noble catalysts in terms of both stability and activity, posing a grand challenge in developing robust OER catalysts. This work establishes a baseline for enhancing the stability of Ru-based OER catalysts in acidic liquid cells and provides a valuable reference for PEM water electrolyzers.

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