Differential Electrochemical Mass Spectrometry Research Articles

Electrochemical reduction of NO3− to NH3 using defect-rich TiO2 support loaded with CuNi catalysts: differential electrochemical mass spectrometry insights

A promising approach for reducing nitrate (NO3−) in water waste is NO3− reutilization to ammonia (NH3). This work investigates the synergistic effect of Cu40Ni60 catalyst on a defect-rich TiO2 (TNSD) carbon vulcan composite (C-TNSD). The study starts with CuNi metallic content pre-screened over carbon vulcan (C) to identify the most promising CuNi ratios for nitrate reduction reaction (NO3-RR) to NH3. This is the case of Cu 20 wt% and Ni 80 wt% (Cu20Ni80), Cu 40 wt% and Ni 60 wt% (Cu40Ni60), Cu 60 wt% and Ni 40 wt% (Cu60Ni40), and Cu 80 wt%, Ni 20 wt% (Cu80Ni20) and Cu/Ni monometallic catalysts. Among these ratios, Cu40Ni60 resulted in the most promising electrocatalyst when loaded over C-TNSD, whose functionality has been assessed using in situ differential electrochemical mass spectrometry (DEMS). The results indicate that Cu40Ni60/C-TNSD attains a similar NH3 selectivity to Cu40Ni60 supported on TiO2-carbon vulcan composites. However, Cu40Ni60/C-TNSD does not hinder charge transport, making it the most suitable electrocatalyst for NH3 production. A synergistic interaction between Cu40Ni60 and C-TNSD is proposed. The results are supported by structural, (electro)chemical, and morphological characterization. From a broader perspective, defective-rich catalysts can be developed to control the electrochemical reaction sequence during NO3-RR.

Regulating Grafting Density to Realize High-Areal-Capacity Silicon Submicroparticle Anodes Under Ultralow Binder Content.

Grafted biopolymer binders are demonstrated to improve the processability and cycling stability of the silicon (Si) nanoparticle anodes. However, there is little systematical exploration regarding the relationship between grafting density and performance of grafted binder for Si anodes, especially when Si particles exceed the critical breaking size. Herein, a series of guar gum grafted polyacrylamide (GP) binders with different grafting densities are designed and prepared to determine the optimal grafting density for maximizing the electrochemical performance of Si submicroparticle (SiSMP) anodes. Among various GP binders, GP5 with recommended grafting density demonstrates the strongest adhesion strength, best mechanical properties, and highest intrinsic ionic conductivity. These characteristics enable the SiSMP electrodes to sustain the electrode integrity and accelerate lithium-ion transport kinetics during cycling, resulting in high capacity and stable cyclability. The superior role of GP5 binder in enabling robust structure and stable interface of SiSMP electrodes is revealed through the PeakForce atomic force microscopy and in situ differential electrochemical mass spectrometry. Furthermore, the stable cyclabilities of high-loading SiSMP@GP5 electrode with ultralow GP5 content (1wt%) at high areal capacity as well as the good cyclability of Ah-level LiNi0.8Co0.1Mn0.1O2/SiSMP@GP5 pouch cell strongly confirms the practical viability of the GP5 binder.

Dialing in the Voltage Window: Reconciling Interfacial Degradation and Performance Decay for Cation-Disordered Rocksalt Cathodes

Li-excess, cation-disordered rocksalt (DRX) cathode materials possess promising electrochemical properties and resource-friendly compositions, making them attractive Li-ion cathode materials. A key drawback of DRX materials is high interfacial reactivity that leads to electrolyte degradation, which ultimately causes a decay in cell performance. In this work, differential electrochemical mass spectrometry (DEMS) is used to study electrolyte degradation processes during initial cycling of DRX cathodes. Comparing outgassing during cycling in six unique voltage windows with upper cutoff voltages of 4.6 or 4.8 V vs Li/Li+ and lower cutoff voltages of 1.5, 1.85, or 2 V vs Li/Li+ reveals the high- and low-voltage processes that separately contribute to degradation at the cathode-electrolyte interface. Charging to high voltages is shown to drive oxidative degradation, consistent with conventional understanding of interfacial reactivity at the cathode-electrolyte interface. Surprisingly, discharging below 2.0 V vs Li/Li+ is also revealed to drive reductive degradation at the same interface, which induces elevated CO2 evolution on the following charge. Subsequently, extended cycling of electrolyte-lean DRX-graphite full-cells shows that performance decay is exacerbated by cycling in voltage ranges that induce interfacial degradation. Post-mortem analysis also indicates notable loss of active Li and dissolution of Mn and Ti from the DRX cathode. Collectively, these analyses demonstrate a clear link between electrolyte degradation and performance decay during cycling of DRX materials. This work highlights the necessity of voltage window optimization to maximize DRX cycling performance and the importance of cell design when evaluating cycling stability.

Synergistic promotion by highly active square-shaped lead oxide and visualized electrolyzer for enhanced electrochemical ozone production

Electrochemical ozone production (EOP) is an intrinsically safe technology compared to Corona discharge methods for ozone generation. However, EOP technology exhibits higher electrical utility demand. Herein, a square-shaped lead oxide (PbOx-CTAB-120) electrocatalyst with outstanding EOP activity has been successfully prepared by a simple method. Then the PbOx-CTAB-120 was assembled into a newly visualized EOP electrolyzer (with parallel flow field) at 1.0 A cm−2 in ultrapure water. The gaseous ozone yield reached 588 mg h−1 g−1catalyst, corresponding to a specific energy consumption (PEOP) of 56 Wh g−1gaseous ozone. In-situ18O isotope-labelled differential electrochemical mass spectrometry reveals that PbOx-CTAB-120 undergoes phase shuttling to β-PbO2via the lattice oxygen oxidation mechanism pathway. Furthermore, density functional theory calculations for multiple reaction pathways on the Pb3O4 (110) surface also demonstrated the participance of lattice oxygen in the EOP process, with the results show that the oxygen vacancy generated from lattice oxygen migration could effectively stabilize the OOH* and O2* reaction intermediate in contrast to the adsorbate evolution mechanism. Therefore, the presence of highly stabilized surfaces Pb3O4 (110) on PbOx-CTAB-120 before phase shuttling and the stabilization of β-PbO2 (101) and β-PbO2 (110) crystalline surfaces after phase shuttling allowed PbOx-CTAB-120 to maintain its excellent EOP activity and stability. Moreover, based on computational fluid dynamics simulations and experimental observations, the parallel flow field design facilitated efficient mass transfer of the gaseous product (O2+O3) and effective thermal dissipation of the system. In addition, the high activity electrocatalyst coupled with the optimized EOP electrolyzer enabled efficient in-situ degradation of organic species.

Elucidating Gas Evolution of Prussian White Cathodes for Sodium‐ion Battery Application: The Effect of Electrolyte and Moisture

AbstractAs global energy storage demand increases, sodium‐ion batteries are often considered as an alternative to lithium‐ion batteries. Hexacyanoferrate cathodes, commonly referred to as Prussian blue analogues (PBAs), are of particular interest due their low‐cost synthesis and promising electrochemical response. However, because they consist of ~50 wt% cyanide anions, a possible release of highly toxic cyanide gases poses a significant safety risk. Previously, we observed the evolution of (CN)2 during cycling via differential electrochemical mass spectrometry (DEMS), but were unable to determine a root cause or mechanism. In this work, we present a systematical investigation of the gas evolution of Prussian white (PW) with different water content via DEMS. While H2 is the main gas detected, especially in hydrated PW and during overcharge (4.6 V vs. Na+/Na), the evolution of CO2 and (CN)2 depends on the electrolyte conductive salt. The use of oxidative NaClO4 instead of NaPF6 is the leading cause for the formation of (CN)2. Mass spectrometric evidence of trace amounts of HCN is also found, but to a much lower extent than (CN)2, which is the dominant safety risk when using NaClO4‐containing electrolyte, which despite being a good model salt, is not a viable option for commercial applications.

Spatial configuration of Fe–Co dual-sites boosting catalytic intermediates coupling toward oxygen evolution reaction

Oxygen evolution reaction (OER) is the pivotal obstacle of water splitting for hydrogen production. Dual-sites catalysts (DSCs) are considered exceeding single-site catalysts due to the preternatural synergetic effects of two metals in OER. However, appointing the specific spatial configuration of dual-sites toward more efficient catalysis still remains a challenge. Herein, we constructed two configurations of Fe-Co dual-sites: stereo Fe-Co sites (stereo-Fe-Co DSC) and planar Fe-Co sites (planar-Fe-Co DSC). Remarkably, the planar-Fe-Co DSC has excellent OER performance superior to stereo-Fe-Co DSC. DFT calculations and experiments including isotope differential electrochemical mass spectrometry, in situ infrared spectroscopy, and in situ Raman reveal the *O intermediates can be directly coupled to form *O-O* rather than *OOH by both the DSCs, which could overcome the limitation of four electron transfer steps in OER. Especially, the proper Fe-Co distance and steric direction of the planar-Fe-Co benefit the cooperation of dual sites to dehydrogenate intermediates into *O-O* than stereo-Fe-Co in the rate-determining step. This work provides valuable insights and support for further research and development of OER dual-site catalysts.

Electrochemical Redox Conversion of Formate to CO via Coupling Fe-Co Layered Double Hydroxides and Au Catalysts.

Formate has been considered an inactive molecule and thus cannot be further reduced under CO2 reduction conditions, which limits its widespread application as feedstock. Here we present an electrochemical redox conversion of formate to CO through the potential-dependent generation of carbon dioxide radical anions (CO2 ⋅- ) on Fe-Co layered double hydroxides (Fe-Co LDHs) and the subsequent reduction of CO2 ⋅- to CO on Au catalysts. We present an electrodeposition protocol for the synthesis of Fe-Co LDHs with precise composition control and find that Fe1 Co4 exhibits a promising potential window for CO2 ⋅- formation between 1.14 and 1.4 V and an optimized potential at 1.24 V at a neutral pH condition. We further determined the formation of CO2 ⋅- at 1.24 V via electron paramagnetic resonance and CO2 at >1.4 V through differential electrochemical mass spectrometry. This work provides a redox chemistry route for converting formate into CO through a coupled slit parallel-plate electrode system.

3D‐Printed Nanostructured Copper Substrate Boosts the Sodiated Capability and Stability of Antimony Anode for Sodium‐Ion Batteries

AbstractSodium‐ion batteries (SIBs) represent a viable substitute to lithium‐ion batteries due to their affordability and resource abundance. For SIBs, antimony (Sb) shows potential as anode material but is impeded by the high volumetric variations. Here the challenges of Sb sodium storage by introducing the nanostructured Cu substrate for enhanced Sb adhesion and morphology optimization is addressed, which is realized by fused deposition modeling (FDM) printing of Cu substrate, subsequent high‐temperature sintering, and electrodeposition of Sb. In SIBs, the Sb deposited on three dimensional (3D) printed Cu substrate performs improved cycling stability compared with that of Sb@Cu with commercial Cu foil substrate, which can be attributed to the nanostructure of the 3D‐Cu substrate. Such architecture of 3D‐Cu induces the generation of pine‐leaf‐like Sb clusters to promote stability and kinetics, and it aids the adhesion between the Sb cluster and 3D‐Cu substrate for preventing the Sb detachment and restructuring the Sb cluster to the robust porous ligament‐channel Sb framework. The morphology evolution, (de)sodiation mechanism, and gas evolution are explored by ex situ scanning electron microscope, operando X‐ray diffraction, and operando differential electrochemical mass spectrometry separately. The developed Sb@3D‐Cu anode offers a flexible pathway for constructing 3D‐printed self‐supported electrodes for SIBs.

Prolonging the Cycle Stability of Anion Redox P3-Type Na0.6Li0.2Mn0.8O2 through Al2O3 Atomic Layer Deposition Surface Modification.

Sodium-ion batteries (SIBs) are becoming an alternative option for large-scale energy storage systems owing to their low cost and abundance. The lattice oxygen redox (LOR), which has the potential to increase the reversible capacity of materials, has promoted the development of high-energy cathode materials in SIBs. However, the utilization of oxygen anion redox reactions usually results in harmful lattice oxygen release, which hastens structural deformation and declines electrochemical performance, severely hindering their practical application. Herein, a ribbon-ordered superstructured P3-type Na0.6Li0.2Mn0.8O2 (NLMO) cathode with a uniform Al2O3 coating through atomic layer deposition (ALD) was synthesized. The cycling stability and rate capability of the materials were improved by a proper thickness of the Al2O3 layer. Differential electrochemical mass spectrometry (DEMS) results clearly suggest that the Al2O3 coating can inhibit the CO2 release caused by the highly active surface of the NLMO material. Moreover, the results of transmission electron microscopy (TEM) and etching X-ray photoelectron spectroscopy (XPS) show that the Al2O3 coating can effectively prevent electrolyte and electrode side reactions and the dissolution of Mn. This surface engineering strategy sheds light on the way to prolong the cycling stability of anionic redox cathode materials.

Functional Composite Dual-Phase In Situ Self-Reconstruction Design for High-Energy-Density Li-Rich Cathodes.

The unique anionic redox mechanism provides, high-capacity, irreversible oxygen release and voltage/capacity degradation to Li-rich cathode materials (LRO, Li1.2Mn0.54Co0.13Ni0.13O2). In this study, an integrated stabilized carbon-rock salt/spinel composite heterostructured layers (C@spinel/MO) is constructed by in situ self-reconstruction, and the generation mechanism of the in situ reconstructed surface is elucidated. The formation of atomic-level connections between the surface-protected phase and bulk-layered phase contributes to electrochemical performance. The best-performing sample shows a high increase (63%) of capacity retention compared to that of the pristine sample after 100 cycles at 1C, with an 86.7% reduction in surface oxygen release shown by differential electrochemical mass spectrometry. Soft X-ray results show that Co3+ and Mn4+ are mainly reduce in the carbothermal reduction reaction and participate in the formation of the spinel/MO rock-salt phase. The results of oxygen release characterized by Differential electrochemical mass spectrometry (DEMS) strongly prove the effectiveness of surface reconstruction.

Recent development and applications of differential electrochemical mass spectrometry in emerging energy conversion and storage solutions.

Electrochemical energy conversion and storage are playing an increasingly important role in shaping the sustainable future. Differential electrochemical mass spectrometry (DEMS) offers an operando and cost-effective tool to monitor the evolution of gaseous/volatile intermediates and products during these processes. It can deliver potential-, time-, mass- and space-resolved signals which facilitate the understanding of reaction kinetics. In this review, we show the latest developments and applications of DEMS in various energy-related electrochemical reactions from three distinct perspectives. (I) What is DEMS addresses the working principles and key components of DEMS, highlighting the new and distinct instrumental configurations for different applications. (II) How to use DEMS tackles practical matters including the electrochemical test protocols, quantification of both potential and mass signals, and error analysis. (III) Where to apply DEMS is the focus of this review, dealing with concrete examples and unique values of DEMS studies in both energy conversion applications (CO2 reduction, water electrolysis, carbon corrosion, N-related catalysis, electrosynthesis, fuel cells, photo-electrocatalysis and beyond) and energy storage applications (Li-ion batteries and beyond, metal-air batteries, supercapacitors and flow batteries). The recent development of DEMS-hyphenated techniques and the outlook of the DEMS technique are discussed at the end. As DEMS celebrates its 40th anniversary in 2024, we hope this review can offer electrochemistry researchers a comprehensive understanding of the latest developments of DEMS and will inspire them to tackle emerging scientific questions using DEMS.

MgO coated P2-Na0.67Mn0.75Ni0.25O2 layered oxide cathode for Na-Ion batteries

In this study, we propose an effective strategy to improve the electrochemical performance of a P2-Na0.67Mn0.75Ni0.25O2 (P2-MNO) cathode material for Na-ion batteries based on MgO surface coating. The MgO coating, with a thickness of ∼20–50 nm, is obtained by means of a facile wet-chemistry approach followed by heat treatment carried out at comparatively low temperatures (400–500 °C) in order to avoid possible Mg doping in the bulk of the P2-MNO. Detailed electrochemical investigations demonstrate improved electrochemical performance of the MgO-coated material (M-P2-MNO) in comparison to pristine bare one at both room and elevated (40 °C) temperatures. Operando differential electrochemical mass spectroscopy (DEMS) demonstrate that the MgO coating is effective in suppressing unwanted gas evolution due to side reactions thus stabilizing the cathode/electrolyte interface.

Suppressing Surface Ligand-to-Metal Charge Transfer toward Stable High-Voltage LiCoO2.

Increasing the charging cutoff voltage is a viable approach to push the energy density limits of LiCoO2 and meet the requirements of the rapid development of 3C electronics. However, an irreversible oxygen redox is readily triggered by the high charging voltage, which severely restricts practical applications of high-voltage LiCoO2. In this study, we propose a modification strategy via suppressing surface ligand-to-metal charge transfer to inhibit the oxygen redox-induced structure instability. A d0 electronic structure Zr4+ is selected as the charge transfer insulator and successfully doped into the surface lattice of LiCoO2. Using a combination of theoretical calculations, ex situ X-ray absorption spectra, and in situ differential electrochemical mass spectrometry analysis, our results show that the modified LiCoO2 exhibits suppressed oxygen redox activity and stable redox electrochemistry. As a result, it demonstrates a robust long-cycle lattice structure with a practically eliminated voltage decay (0.17 mV/cycle) and an excellent capacity retention of 89.4% after 100 cycles at 4.6 V. More broadly, this work provides a new perspective on suppressing the oxygen redox activity through modulating surface ligand-to-metal charge transfer for achieving a stable high-voltage ion storage structure.

Quantitative Analysis of CO2 Evolution in an Alkaline Electrolyte Solution By Differential Electrochemical Mass Spectroscopy

CO2 is involved in various main and side reactions of electrochemical energy devices, such as carbon corrosion reactions and alcohol oxidation reactions. Differential electrochemical mass spectroscopy (DEMS) has been intensively applied in acidic electrolyte solutions to analyze these reactions. DEMS is the in-situ electrochemical measurement technique to analyze volatile species with the mass spectrometer (MS). However, the applications of DEMS to alkaline electrolyte solutions have been limited due to the high solubility of CO2 in alkaline solutions. While "conventional DEMS cells," where porous thin-film working electrodes are formed onto polytetrafluoroethylene (PTFE) membrane interface, can quantitatively analyze CO2 that has not dissolved into the electrolyte yet [1], the working electrode materials are limited to those that can be deposited on porous PTFE membrane as porous thin-films. Recently, Möller et al. have developed the DEMS system, which can detect CO2 from general planer electrodes coated by catalyst powders by combining a neutralizer and "dual thin-layer flow cell" [2]. However, due to the relatively low detection limit, quantitative analysis of evolved CO2 has not been accomplished. In this study, we attempt to use high surface area electrodes to enhance the MS signal of CO2 to enable quantitative analysis of evolved CO2. To suppress the in-plane reaction distribution in the flow cell, we integrated an anion exchange membrane into the cell and arranged the counter electrode opposing the working electrode [3] (Fig. 1 (a)).CO-stripping voltammetry was performed to evaluate the CO2 detectability of the constructed DEMS system. The DEMS cell was composed of a commercial Pt/C electrode as the working electrode, a commercial Hg/HgO electrode as the reference electrode, a Pt mesh as the reference electrode, 1 mol dm–3 KOH aq as the electrolyte solution, and 1 mol dm–3 H2SO4 aq as the neutralizer. Figure 1 (b) shows the CO-stripping voltammogram and corresponding MS signal of CO2 (m/z = 44). MS signal of CO2 accompanied by the anodic CO oxidation current is clearly observed from 0.6 to 1.2 V vs. RHE. The calibration constant, which correlates the MS signal of CO2 to partial current for CO2 evolution reaction, is successfully obtained as 2.2 × 10–10, which shows that the DEMS system established in this study can quantitatively analyze CO2. Applications to the carbon corrosion reactions are also presented at the site.

(Invited) A Novel Dems Approach for Studying Gas Evolution in Pouch Cells

In this study, we designed a novel differential electrochemical mass spectrometry (DEMS) system to in-situ quantify the gas generation in batteries. While a lot of battery gas analyses were carried out by DEMS previously, most of those studies were based on small coin cells or EL cells. The fluid electrolyte and limited amount of active material may make it challenging to quantify the gas generation. The DEMS we designed here can continually sample gas from a small 2.5Ah pouch cell, and it has a similar electrolyte to capacity ratio, 1.8g/Ah, with our production cell. To the best of our knowledge, this is the first DEMS design based on a pouch cell.Moreover, by using flowrate-controlled Ar carrier gas and a reasonable residence time setup, our DEMS design not only can identify volatile electrolyte degradation products throughout battery cycling but also quantify the gaseous species production rates as a function of the state of charge. We found that cell chemistry and operation protocol greatly impact gas product species, the production profile of different gases during cycling, and the total gas quantity. For example, the gas evolution of oxidation products, such as CO2 and CO, is exacerbated by the elevated upper cutoff voltage, while reduction products are only minimally affected. Furthermore, changing the electrolyte SEI former, from EC to FEC, or adding different electrolyte additives can affect the gas product species generation dramatically as well.Therefore, we successfully demonstrated DEMS as a powerful tool to probe the gas evolution behavior in different applications-based batteries, provided valuable data for battery reactivity simulation, and most importantly, provided guidance for electrolyte optimization.

Electrochemical Analysis of Charge Overpotentials in Non-Aqueous Lithium and Sodium Oxygen Batteries

Aprotic metal-oxygen batteries, especially Li-O2 and Na-O2 batteries, could afford theoretical specific energies of more than 500 Wh/kg. However, while not compromising on rechargeability, the practical realization of the theoretically possible high specific energies has been elusive. A better understanding of the differences and similarities between Li–O2 and Na–O2 battery systems in terms of charge-discharge mechanisms and parasitic chemistry will be meaningful in solving these challenges. Here, we explore the differences between the two systems using a combination of galvanostatic charge-discharge measurements, Differential Electrochemical Mass spectrometry (DEMS), and Potentiostatic Electrochemical Impedance Spectroscopy (PEIS) analysis. The discharge profiles of these battery chemistries are similar in terms of overpotential and have been widely studied. But the origins of the differences in charge overpotentials are not clear. Using in-situ pressure decay measurements during discharge, we calculated the number of electrons/oxygen (e-/O2) to be 2.02 and 1.01 for Li-O2 and Na-O2 cells, respectively. Further, DEMS analysis during charge has shown that the ideal 2 e-/O2 is attained only during the initial phases of charging for Li-O2 cells. However, for Na-O2, the ideal 1 e-/O2 is achieved during a signification portion of the galvanostatic charge step. We corroborate these findings with PEIS and distribution of relaxation times (DRT) analysis to develop a mechanistic view of the processes that lead to poor coulombic and oxygen evolution efficiencies in metal-oxygen cells. Based on DRT analysis, we identify a lower time constant process that is common to both Li-O2 and Na-O2 cells. Interestingly, we observed that voltage polarization is preceded by the observation of this lower time constant peak. In the case of Li-O2 cells, this lower time constant process was observed at the end of discharge and throughout the recharge process, while for the Na-O2 cells, this was only observed after about 70% of recharge. We discuss the possible origins of this low time-constant process and its implications for recharging metal-oxygen batteries. We will also discuss the role of singlet oxygen, if any, in the recharge efficiencies of these two aprotic metal-oxygen batteries. Our results imply that the identification of the origins of this lower time constant process and possible suppression of this process will be key for rechargeable metal-oxygen batteries.

Tortuosity Effect of Graphite Anodes for High-Performance Cylindrical Li-Ion Batteries

This study aimed to investigate the impact of graphite tortuosity at the practical thick electrode level, which is complex and not yet well understood, on the electrochemical performance of Ni-rich NCA90 Li-ion batteries (LIBs). Various graphite anode tortuosities were examined, and it was found that low-tortuosity electrodes demonstrated better graphite utilization than high-tortuosity electrodes. In operando X-ray Diffraction and Differential Electrochemical Mass Spectrometry were also employed for charge storage mechanism and gas evolution detection, respectively. We have found that the tortuosity of the graphite electrode had an impact on the amount of Li present in the lithiated graphite phase due to diffusion limitations. However, graphite tortuosity did not have an influence on gas generation during battery operation. Safety testing conducted according to UN38.3 confirms all batteries produced in this work are safe. The study eventually demonstrated the practical use of NCA90 LIB cells optimized with varying tortuosities of thick graphite electrodes in a high-performance Lamborghini GoKart. By integrating fundamental research with practical demonstrations, this investigation is expected to contribute to further advancements in Ni-rich LIB technology.

Assessing the Stability of Co3O4 Under Oxygen Evolution Reaction Conditions at Low and Mild pH

Water and CO2 electrolysis will play a crucial role in converting renewable energy into value-added chemicals and chemical fuels. To successfully employ and expand these technologies globally, ideally, one should develop Earth-abundant, cost-effective catalysts with high activity and stability. The requirements for the catalysts depend on the configuration of the electrolyzer, and the electrolyte used there. However, especially in CO2 electrolysis, the stability of the catalyst in a certain electrolyte does not guarantee its successful use on a long-term scale, as the pH in the electrolyzer may change during long-term experiments due to ion transfer through the membrane.1 The anode materials should, therefore, be stable across a broad pH range and/or in carbonate-rich electrolytes. Although the earth-abundant, non-noble transition metals, and their compounds are highly stable at higher pH, they are less stable than Ir or Pt at low and (near-)neutral pH.2 Interestingly, recent studies have shown that Co-based oxides exhibit promising stability even at low pH.3, 4 However, the nature of this stability as well as the mechanisms of non-noble metal oxides catalyzing OER at low or near-neutral pH, are yet to be discovered. In this work, we analyze the stability of cobalt oxide under various electrochemical conditions at low pH with the use of a scanning flow cell (SFC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) and differential electrochemical mass spectrometry (DEMS). By using these techniques, we can follow the dissolution of Co online and find potential narrow stability windows before and during the oxygen evolution reaction (OER). Benefiting from the obtained results, mitigating strategies for minimizing Co dissolution are proposed and discussed.

Designing a Novel Setup for High-Throughput Investigations of Electrochemical Reactions in Real Time

With the great interest in new electrochemical processes, fast screening of various reaction parameters is highly desirable. For this purpose, differential electrochemical mass spectrometry (DEMS) and membrane-inlet mass spectrometry (MIMS) have been established to enable real-time monitoring of volatile compounds. However, the analysis of non-volatile compounds is commonly limited by the temporal resolution of traditional quantification methods such as NMR, GC-MS, or LC-MS. While ambient ionization mass spectrometry (AIMS) generally enables time-resolved monitoring of non-volatile compounds, electrolyte salts can lead to ionization suppression. The latter can decrease the sensitivity of product detection and the reliability of quantitative data. Therefore, a suitable reaction setup and thorough investigations are needed when utilizing AIMS. Nonetheless, in recent efforts, an electrochemical flow cell was coupled with such a technique to provide a method for on-line monitoring of non-voltile reaction products in aqueous electrolytes. To keep up with the increasing interest in electrosynthesis in organic media, we now present a new setup that is also applicable to non-aqueous media. It pairs a novel and versatile electrochemical cell with an AIMS and DEMS for highly sensitive detection of reaction products. Moreover, various reaction parameters such as electrode material, electrolyte, and temperature can be investigated in high-throughput.Key words: Electrocatalysis, Electrosynthesis, Real-time, On-line monitoring, High-throughput

Electrocatalytic Conversion of Glucose into Hydrogen and Value-Added Compounds on Gold and Nickel Catalysts

Fine chemistry historically relies on the fossil fuel industry, implying oil extraction and refining [1]. The rarefaction of this resource and adverse environmental consequences of its extraction motivate research for alternative sources of chemicals. Low carbon footprint chemicals can be synthesized from nonedible biomass waste [2]; cellulose extracted from biomass can therefore play an important role, being a clean and widely accessible carbon source. One can extract D-Glucose (units that constitute cellulose) from cellulose and obtain numerous chemicals of interest, such as sorbitol [3][4] or gluconic acid [5][6] (gluconate in alkaline media), respectively by selective reduction or oxidation.Searching for high-performance non-enzymatic catalysts to perform such reactions brought us to study the activity and selectivity of gold and nickel in alkaline media. At the anode, results from differential electrochemical mass spectrometry (DEMS) seem to indicate that the glucose oxidation on a gold surface initiates by its dissociative adsorption (dehydrogenation): the dihydrogen (H2) produced likely originates from the formation of metastable H adsorbates (Had) [7] that diffuse onto the surface [8] and recombine into H2. In parallel, the adsorbed glucose oxidizes into value-added products such as gluconic acid, through a mechanism proposed from in situ (Fourier Transform InfraRed spectroscopy, FTIR) and ex situ (products analysis by High Performance Liquid Chromatography, HPLC) observations, and on the evaluation of the number of exchanged electrons using the rotating ring disk electrode (RRDE). Confronting the experimental data to a microkinetics model enables to validate the proposed mechanism and to estimate the kinetics rate constants. At the cathode, the glucose reduction reaction (GRR) into sorbitol competes with the hydrogen evolution reaction (HER). The HER activity of nickel strongly depends on its surface oxidation state [9], which can be tuned to search the best selectivity towards sorbitol. Combining high value-added compounds production with H2 as by-product allows to improve the overall energy efficiency of this electrolysis.[1] P. G. Levi and J. M. Cullen, “Mapping global flows of chemicals: from fossil fuel feedstocks to chemical products,” Environ. Sci. Technol., vol. 52, no. 4, pp. 1725–1734, 2018, doi: 10.1021/acs.est.7b04573.[2] D. Saygin, D. J. Gielen, M. Draeck, E. Worrell, and M. K. Patel, “Assessment of the technical and economic potentials of biomass use for the production of steam, chemicals and polymers,” Renew. Sustain. Energy Rev., vol. 40, pp. 1153–1167, 2014, doi: 10.1016/j.rser.2014.07.114.[3] B. García, J. Moreno, G. Morales, J. A. Melero, and J. Iglesias, “Production of sorbitol via catalytic transfer hydrogenation of glucose,” Appl. Sci., vol. 10, no. 5, 2020, doi: 10.3390/app10051843.[4] X. Guo et al., “Selective hydrogenation of D-glucose to D-sorbitol over Ru/ZSM-5 catalysts,” Chinese J. Catal., vol. 35, no. 5, pp. 733–740, May 2014, doi: 10.1016/S1872-2067(14)60077-2.[5] H. S. Isbell, H. L. Frush, and F. J. Bates, “Manufacture of calcium gluconate by electrolytic oxidation of dextrose,” Ind. Eng. Chem., vol. 24, no. 4, pp. 375–378, 1932, doi: 10.1021/ie50268a003.[6] S. Anastassiadis and I. Morgunov, “Gluconic acid production,” Recent Pat. Biotechnol., vol. 1, no. 2, pp. 167–180, May 2007, doi: 10.2174/187220807780809472.[7] M. M. Jaksic, B. Johansen, and R. Tunold, “Electrochemical behaviour of gold in acidic and alkaline solutions of heavy and regular water,” Int. J. Hydrogen Energy, vol. 18, no. 2, pp. 91–110, Feb. 1993, doi: 10.1016/0360-3199(93)90196-H.[8] J. Cornejo-Romero, A. Solis-Garcia, S. M. Vega-Diaz, and J. C. Fierro-Gonzalez, “Reverse hydrogen spillover during ethanol dehydrogenation on TiO2-supported gold catalysts,” Mol. Catal., vol. 433, pp. 391–402, 2017, doi: 10.1016/j.mcat.2017.02.041.[9] A. G. Oshchepkov et al., “Nanostructured nickel nanoparticles supported on vulcan carbon as a highly active catalyst for the hydrogen oxidation reaction in alkaline media,” J. Power Sources, vol. 402, no. June, pp. 447–452, 2018, doi: 10.1016/j.jpowsour.2018.09.051. Figure 1