Electrochemical water splitting is one of the most promising approaches for sustainable energy conversion and storage toward a future hydrogen society. This demands durable and affordable ...electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In this study, we report the preparation of uniform Ni-P-O, Ni-S-O, and Ni-S-P-O electrocatalytic films on nickel foam (NF) substrates
via
flow cell-assisted electrodeposition. Remarkably, electrodeposition onto 12 cm
2
substrates was optimized by strategically varying critical parameters. The high quality and reproducibility of the materials is attributed to the use of a 3D-printed flow cell with a tailored design. Then, the as-fabricated electrodes were tested for overall water splitting in the same flow cell under alkaline conditions. The best-performing sample, NiSP/NF, required relatively low overpotentials of 93 mV for the HER and 259 mV for the OER to produce a current density of 10 mA cm
−2
. Importantly, the electrodeposited films underwent oxidation into amorphous nickel (oxy)hydroxides and oxidized S and P species, improving both HER and OER performance. The superior electrocatalytic performance of the Ni-S-P-O films originates from the unique reconstruction process during the HER/OER. Furthermore, the overall water splitting test using the NiSP/NF couple required a low cell voltage of only 1.85 V to deliver a current density of 100 mA cm
−2
. Overall, we demonstrate that high-quality electrocatalysts can be obtained using a simple and reproducible electrodeposition method in a robust 3D-printed flow cell.
A reproducible and efficient electrodeposition method in a 3D-printed flow cell is used to synthesize high-quality Ni-S-P-O films on nickel foam for overall water splitting.
The electrochemical oxidation of sulfite ions offers encouraging advantages for large-scale hydrogen production, while sulfur dioxide emissions can be effectively used to obtain value-added ...byproducts. Herein, the performance and stability during sulfite electrolysis under alkaline conditions are evaluated. Nickel foam (NF) substrates were functionalized as the anode and cathode through electrochemical deposition of palladium and chemical oxidation to carry out the sulfite electro-oxidation and hydrogen evolution reactions, respectively. A combined analytical approach in which a robust electrochemical flow cell was coupled to different in situ and ex situ measurements was successfully implemented to monitor the activity and stability during electrolysis. Overall, satisfactory sulfite conversion and hydrogen production efficiencies (>90%) at 10 mA·cm–2 were mainly attributed to the use of NF in three-dimensional electrodes with a large surface area and enhanced mass transfer. Furthermore, stabilization processes associated with electrochemical dissolution and sulfur crossover through the membrane induced specific changes in the chemical and physical properties of the electrodes after electrolysis. This study demonstrates that NF-based electrocatalysts can be incorporated in an efficient electrochemical flow cell system for sulfite electrolysis and hydrogen production, with potential applications at a large scale.
Flow devices fabricated by means of 3D-printing offer an economic and effective approach for testing different electrochemical systems at the laboratory scale. Here, the fabrication and optimization ...of a novel filter-press electrochemical reactor is described. 3D-printing is used to obtain critical components of the device as a sustainable and efficient manufacturing approach. Hydrodynamics and mass transfer of different flow distributors, turbulence promoters, and nickel foam, as a three-dimensional (3D) electrode, were evaluated by a convenient set of well-known techniques for filter-press reactor characterization. Furthermore, the chemical stability of 3D-printed materials was assessed in several electrolytes used for common electrochemical applications. Designed configurations and geometries exhibited enhanced turbulence and large mass transfer coefficients, which make them adequate for processes such as electrosynthesis, electrodeposition, and electrochemical water splitting. Ultimately, superior performance was validated for nickel foam, demonstrating robustness of the reactor for realistic evaluation of electrocatalytic materials. Therefore, the proposed electrochemical reactor provides a low-cost and versatile alternative for testing electrochemical systems in a wide range of applications.
Sulfur-based thermochemical cycles, such as the hybrid sulfur-ammonia (HySA) cycle, offer a valuable approach in which hydrogen is produced by exploiting sulfur dioxide (potentially pollutant ...emissions) through the electrochemical oxidation of aqueous sulfite. In this study, the effect of pH on electrooxidation rate was assessed by comparing different reaction scenarios. Then, a Central Composite Design (CCD) combined with a Response Surface Methodology (RSM) was used to optimize batch electrooxidation of ammonium sulfite at near-neutral pH. Results show that the use of an anion exchange membrane (AEM) greatly improves sulfite electrooxidation rate while pH is effectively stabilized. Furthermore, a second-order model that relates applied potential and sulfite concentration with the normalized half-life of the reaction was obtained and verified experimentally at long-term batch electrooxidations. A good agreement between the model and experimental tests, adequate hydrogen recoveries and low sulfur crossover through the membrane demonstrate practical robustness of this approach.
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•Batch electrooxidation of ammonium sulfite is optimized at slightly alkaline media.•pH is stabilized in an electrochemical reactor by means of an anion exchange membrane.•A second-order model for electrooxidation rate estimation is obtained.•Long-term electrooxidation tests demonstrate robustness of the approach.
Metallic vanadium carbide (V8C7) with cubic symmetry is examined as an oxygen evolution reaction (OER) precatalyst in alkaline media. Herein, we used quasi in situ scanning electron microscopy and ...energy-dispersive X-ray spectrometry to investigate the structural transformation of the precatalyst V8C7 microparticles during extended cyclic voltammetric (CV) OER testing. Interestingly, an anisotropic morphological transformation (from a distorted sphere to a cuboid) of V8C7 was observed. Our theoretical and experimental results strongly suggest that this morphological change happens due to the selective self-oxidation and dissolution of the V8C7(110) and (111) surfaces and the subsequent exposure of the relatively stable (100), (010), and (001) surfaces. These results also suggest that these stable facets are preferable for the OER, and a current density of 10 mA·cm–2 was delivered at an overpotential of 503 mV after the extended CV OER testing.
Nickel-based materials are widely used as critical components of electrochemical energy devices, including alkaline electrolyzers, capacitors, and alkaline batteries. These materials are often ...preferred because of their availability and low cost compared to precious metals, which makes them excellent candidates for accomplishing the decarbonization goals and electrifying our society. However, several studies have demonstrated that the incorporation of trace impurities from commercial alkaline electrolytes induces significant changes in the intrinsic activity, pseudocapacitance, and stability of Ni-based materials, resulting in erroneous descriptions of their performance. Thus, having a better understanding of the effects of these impurities will lead to practical ways to prevent or control their impact on electrochemical energy devices. In this work, we study the incorporation of transition metals ( i.e., Fe, Co, Cu) that form insoluble hydroxides in alkaline media over nickel (oxy) hydroxide electrocatalysts. We systematically examine how these trace impurities modify the OER activity, stability, and the pseudocapacitive properties of NiOOH. As depicted in Figure 1 , KOH electrolytes containing trace impurities of Fe and Co induce significant changes in the OER onset potential of Ni(OH) 2 /NiOOH electrocatalysts, according to the irreversible charge increase measured through coulovoltammetry (QV) curves. Moreover, distinct redox peaks can be seen for each scenario. After aging in purified KOH electrolyte ( Fig. 1a ), the cyclic voltammogram (CV) of Ni(OH) 2 /NiOOH exhibits four oxidation peaks that can be ascribed to a mixture of both α and β structural phases ( Fig. 1b ) while aging in Fe-unpurified KOH promotes the α phase and shifts the redox peak anodically ( Fig. 1c ). Aging in Co-unpurified KOH promotes a more ordered β structural phase without changing the OER activity significantly ( Fig. 1d ), which is desirable for pseudocapacitive materials. Additional experiments examining the OER activity, stability, and capacitance provide valuable insights into these impurities, and specific strategies to prevent and minimize their effects will be discussed. Overall, this work illustrates the importance of tracking trace metal impurities in alkaline electrolytes to minimize undesirable effects in electrochemical energy devices. Figure 1
In energy conversion devices such as electrolyzers and batteries, the monitoring of electrode surfaces during electrochemical processes is essential to understand their operation mechanisms. One of ...the promising techniques is in situ Raman spectroscopy, which can analyze (i) electrode surface structure, (ii) surface species (reaction intermediate species), and (iii) localized electrolyte species. 1 The bottleneck for using this technique is the high cost and complexity of commercially available electrochemical cells designed for in situ Raman spectroscopy. To solve these issues, a few research groups provided 3D-printed spectroelectrochemical cells with low cost and less complexity. 2,3 However, the spectroelectrochemical cells so far reported require a specific sample type (i.e., particles). We need a low-cost and less-complex spectroelectrochemical cell that can be used for more varieties of samples. In this study, we will provide a new design of a spectroelectrochemical cell that has compatibility with various sample types i.e., substrates (e.g., metal foil strips, fluorine-doped tin oxide-coated glass, indium tin oxide-coated glass, etc.) and particle. Specifically, a versatile, low-cost, and less-complex electrochemical cell for in situ Raman spectroscopy will be fabricated using a stereolithography (SLA) 3D printer with resin as a printing material. Herein, using the SLA 3D-printed spectroelectrochemical cell, we will also demonstrate a few example studies for electrolyzer and battery applications. References W. Zheng, Chemistry–Methods , 3 , e202200042 (2023). M. F. dos Santos et al., Anal. Chem. , 91 , 10386–10389 (2019). G. D. da Silveira et al., Anal. Chim. Acta , 1141 , 57–62 (2021).
Alkaline electrolytes represent a critical component of electrochemical energy devices, including alkaline electrolyzers, fuel cells, supercapacitors, and alkaline batteries. In addition, these ...electrolytes define essential properties of electrocatalytic reactions, such as the oxygen evolution reaction (OER), the hydrogen evolution reaction (HER), and the oxygen reduction reaction (ORR). However, alkaline electrolyte concentrations and compositions are often considered trivial, resulting in misinterpretation of different phenomena and overestimating critical performance metrics. Thus, in an expanding field full of interdisciplinary research groups, there is an urgent need for standardized protocols designed to improve and evaluate the quality of alkaline electrolytes so that electrochemical energy systems can be objectively examined and compared.
In this work, we propose a protocol composed of six steps to prepare, characterize and validate the quality of common alkaline electrolytes. By adapting well-established methods in the literature and validating additional features experimentally, we standardize six general practices: (1) proper alkaline electrolyte handling and preparation, (2) removal of Fe impurities, (3) alkali molarity standardization
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pH titrations, (4) electrolyte composition analysis
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inductively-coupled plasma mass spectrometry (ICP-MS), (5) statistical quality control assessment and (6) electrolyte validation through electrochemical aging of Ni electrodes in alkaline media. The effects of Fe incorporation for different alkaline electrolytes were examined using Ni and NiFe foam electrodes. Furthermore, ICP-MS measurements were complemented with prolonged cyclic voltammetry tests to confirm the effectiveness of the Fe purification procedure. We believe this work illustrates the importance of standardizing protocols and reporting reliable quality metrics to improve consistency and accuracy in electrochemistry. Furthermore, adopting the practices presented in this work would greatly benefit the evaluation and comparison of electrochemical energy materials and devices operating with alkaline electrolytes.
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