Self-activated anodic nanoporous stainless steel electrocatalysts with high durability for the hydrogen evolution reaction

Tuning Stainless Steel Oxide Layers through Potential Cycling─AEM Water Electrolysis Free of Critical Raw Materials

Anion exchange membrane water electrolyzers (AEMWEs) have an intrinsic advantage over acidic proton exchange membrane water electrolyzers through their ability to use inexpensive, stable materials such as stainless steel (SS) to catalyze the sluggish oxygen evolution reaction (OER). As such, the study of active oxide layers on SS has garnered great interest. Potential cycling is a means to create such active oxide layers in situ as they are readily formed in alkaline solutions when exposed to elevated potentials. Cycling conditions in the literature are rife with unexplained variations, and a complete account of how these variations affect the activity and constitution of SS oxide layers remains unreported, along with their influence on AEMWE performance. In this paper, we seek to fill this gap in the literature by strategically cycling SS felt (SSF) electrodes under different scan rates and ranges. The SSF anodes were rapidly activated within the first 50 cycles, as shown by the 10-fold decline in charge transfer resistance, and the subsequent 1000 cycles tuned the metal oxide surface composition. Cycling the Ni redox couple (RC) increases Ni content, which is further enhanced by lowering the cycling rate, while cycling the Fe RC increases Cr content. Fair OER activity was uncovered through cycling the Ni RC, while Fe cycling produced SSF electrodes active toward both the OER and the hydrogen evolution reaction (HER). This indicates that inert SSF electrodes can be activated to become efficient OER and HER electrodes. To this effect, a single-cell AEMWE without any traditional catalyst or ionomer generated 1.0 A cm-2 at 1.94 V ± 13.3 mV with an SSF anode, showing a fair performance for a cell free of critical raw materials.

Metal Electrocatalysts for Hydrogen Production in Water Splitting

The rising demand for fossil fuels and the resulting pollution have raised environmental concerns about energy production. Undoubtedly, hydrogen is the best candidate for producing clean and sustainable energy now and in the future. Water splitting is a promising and efficient process for hydrogen production, where catalysts play a key role in the hydrogen evolution reaction (HER). HER electrocatalysis can be well performed by Pt with a low overpotential close to zero and a Tafel slope of about 30 mV dec-1. However, the main challenge in expanding the hydrogen production process is using efficient and inexpensive catalysts. Due to electrocatalytic activity and electrochemical stability, transition metal compounds are the best options for HER electrocatalysts. This study will focus on analyzing the current situation and recent advances in the design and development of nanostructured electrocatalysts for noble and non-noble metals in HER electrocatalysis. In general, strategies including doping, crystallization control, structural engineering, carbon nanomaterials, and increasing active sites by changing morphology are helpful to improve HER performance. Finally, the challenges and future perspectives in designing functional and stable electrocatalysts for HER in efficient hydrogen production from water-splitting electrolysis will be described.

Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments

Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the 'junctions' between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Degradation of 2-Naphthol in Aqueous Solution by Electro-Fenton System with Cu-Supported Stainless Steel Electrode

For the treatment of 2-naphthol wastewater, the homogeneous electro-Fenton process was considered as an effective method but some disadvantages greatly restrict its application. The three-dimensional electro-Fenton (3D-EF) system using a nano zero-valent iron-supported biochar (NZVIs-BC) particle electrode and a Cu-supported stainless steel electrode (Cu-SSE) was proposed to avoid the disadvantages of the homogeneous electro-Fenton. In this work, the 3D-EF system was developed, which consisted of a Cu-SSE (cathode), a graphite rod (anode) and a NZVIs-BC particle electrode. The effect of the ratio of ferrous sulfate heptahydrate (FS) to rice straw (RS), CuSO4•5H2O amount, initial pH of 2-naphthol wastewater and current intensity (the output current of the power supply) on the removal rate of 2-naphthol were investigated. It is noteworthy that more than 98.36% of the 2-naphthol in aqueous solution was removed by the 3D-EF system, and only about 60.09% of 2-naphthol was removed by the homogeneous electro-Fenton system. Furthermore, naphthalene, benzoic acid, β-naphthoquinone, 1, 2-naphthalenedione, phenol and aromatic hydrocarbon were the main degradation products of 2-naphthol by the 3D-EF system; the toxicity of 2-naphthol wastewater was also greatly reduced.

Recent advances in cobalt-based catalysts for efficient electrochemical hydrogen evolution: a review

Hydrogen (H2) is a new type of renewable energy that can meet people's growing energy needs and is environmentally friendly. In order to improve the industrial application prospect and electrochemical...

Controlled Synthesis and Structural Modulation to Boost Intrinsic Photocatalytic Activity of BiVO4

Modulation of the structure, composition, and morphology through a simple refinement of the synthetic parameters are central to obtaining signature catalytic properties, enabling an understanding of the underlying growth and...

Surface Modification of Electrocatalyst for Optimal Adsorption of Reactants in Oxygen Evolution Reaction

Technological development after the industrial revolution has improved the quality of human life, but global energy consumption continues to increase due to population growth and the development of fossil fuels. Therefore, numerous studies have been conducted to develop sustainable long-term and renewable alternative energy sources. The anodic electrode, which is one of the two-electrode system components, is an essential element for effective energy production. In general, precious metal-based electrocatalysts show high OER reactions from the anodic electrode, but it is difficult to scale up due to their low abundance and high cost. To overcome these problems, transition metal-based anodic electrodes, which exhibit advantages with respect to their low cost and high catalytic activities, are in the spotlight nowadays. Among them, stainless steel is a material with a high ratio of transition metal components, i.e., Fe, Ni, and Cr, and has excellent corrosion resistance and low cost. However, stainless steel shows low electrochemical performance due to its slow sluggish kinetics and lack of active sites. In this study, we fabricated surface modified electrodes by two methods: (i) anodization and (ii) hydrogen peroxide (H2O2) immersion treatments. As a result of comparing the two methods, the change of the electrode surface and the electrochemical properties were not confirmed in the H2O2 immersion method. On the other hand, the porous electrode (PE) fabricated through electrochemical anodization shows a low charge transfer resistance (Rct) and high OER activity due to its large surface area compared to the conventional electrode (CE). These results confirm that the synthesis process of H2O2 immersion is an unsuitable method for surface modification. In contrast, the PE fabricated by anodization can increase the OER activity by providing high adsorption of reactants through surface modification.

Stable Surface Technology for HER Electrodes

With the rapid increase in energy consumption worldwide, the development of renewable and alternative energy sources can sustain long-term development in the energy field. Hydrogen (H2), which is one of the clean chemical fuels, has the highest weight energy density and its combustion byproduct is only water. Among the various methods of producing hydrogen source, water electrolysis is a process that can effectively produce H2. However, it is difficult for commercialization of water electrolysis for H2 production due to the high cost and low abundance of noble metal-based cathodic electrode used for highly efficiency. Several studies have been conducted to reduce noble metal loading and/or completely replace them with other materials to overcome these obstacles. Among them, stainless steel contains many components of transition metals (Ni, Cr, Co) but have sluggish reaction kinetics and small active surface area. In this study, the problem of stainless steel was to be solved by utilizing the electrocatalytic properties of silver nanoparticles on the electrode surface, and electrodes were easily fabricated through the electrodeposition process. In addition, the surface shape, elemental properties, and HER activity of the electrode was analyzed by comparing it with the commercialized silver nanoparticle-coated invasive electrodes from Inanos (Inano-Ag-IE) through the plasma coating process. As a result, silver nanoparticle-coated conventional electrode (Ag-CE) fabricated through electrodeposition confirmed high HER activity and stability. However, the Inano-Ag-IE showed low HER activity as silver nanoparticles were not found. We encourage further research on the production process of such products for sustainable energy applications.

Enhanced Electrocatalytic Activity of Stainless Steel Substrate by Nickel Sulfides for Efficient Hydrogen Evolution

Water splitting is one of the efficient ways to produce hydrogen with zero carbon dioxide emission. Thus far, Pt has been regarded as a highly reactive catalyst for the hydrogen evolution reaction (HER); however, the high cost and rarity of Pt significantly hinder its commercial use. Herein, we successfully developed an HER catalyst composed of NiSx (x = 1 or 2) on stainless steel (NiSx/SUS) using electrodeposition and sulfurization techniques. Notably, the electrochemical active surface area(ECSA) of NiSx/SUS was improved more than two orders of magnitude, resulting in a considerable improvement in the electrochemical charge transfer and HER activity in comparison with stainless steel (SUS). The long-term HER examination by linear scan voltammetry (LSV) confirmed that NiSx/SUS was stable up to 2000 cycles.