W Doping in Ni12P5 as a Platform to Enhance Overall Electrochemical Water Splitting

Plasma-driven integration of multifunctional active sites in three-dimensional self-supported catalysts for enhanced alkaline and seawater splitting

Regulating the structure and composition is an important strategy to obtain high efficiency electrocatalyst. Herein, this paper proposes an innovative plasma-assisted approach to synthesize an efficient electrocatalyst with multiple active components (Co nanoparticles, oxygen vacancies, and CoFe layered double hydroxide nanosheets) covered on CoP nanowire array (denoted as PD-CoFe LDH@CoP, 'PD' is defined as plasma-driven approach) for alkaline water/seawater splitting. The hierarchical nanostructure can endow the catalyst with more substantial mass transfer and expose more active sites. In contrast, the multiple active components can accelerate the electrocatalytic kinetics, making the PD-CoFe LDH@CoP electrocatalyst exhibit excellent catalytic activity. As a result, when assembling a two-electrode system, the assembled cell only needs an ultralow voltage of 1.79 V to reach 100 mA/cm2 in 1 M KOH seawater, together with remarkable durability. This work not only sheds light on an environmentally friendly, economical, and controlled way of fabricating multi-component heterostructure for hydrogen production but also paves the way for future research and development in this promising field.

Phase regulation of Ni(OH)2 nanosheets induced by W doping as self-supporting electrodes for boosted water electrolysis

Developing high-performance and low-cost electrodes for hydrogen and oxygen evolution reactions (HER and OER, respectively) represents a pivotal challenge in the field of water electrolysis. Herein, W doped NiFe LDH nanosheets (NiFe-Wx/NF) were immobilized on nickel foam (NF) through one-step corrosion engineering, which induced the coexistence of α-Ni(OH)2 and β-Ni(OH)2. The doping of large atomic radius W influenced the growth of crystal planes of Ni(OH)2, promoting the formation of α-Ni(OH)2, which results in large layer spaces and neatly arranged nanosheets structure. The optimized NiFe-W0.5/NF catalyst require potentials of only 69 to attain 10 mA/cm2 for HER, and require overpotentials of 269 mV to reach 100 mA/cm2 current density for OER, respectively. The W6+ with high oxidation state can withdraw neighboring electrons from Ni, altering the adsorption energy of hydrogen intermediates, which improves the Volmer step and electrical conductivity in HER. And the large layer space of α-Ni(OH)2 in NiFe-W0.5/NF can be contributed to accelerating the formation of high valence γ-NiOOH, which can accelerate OER kinetics. In addition, the NiFe-W0.5/NF catalyst also provides an overall water splitting activity of 780 mA/cm2 current density at a cell voltage of only 1.90 V, and remains highly stable for over 70 h at 100 mA/cm2, which makes it a bifunctional efficient catalyst for water electrolysis.

Exploring the properties, types, and performance of atomic site catalysts in electrochemical hydrogen evolution reactions

Atomic site catalysts (ASCs) have recently gained prominence for their potential in the electrochemical hydrogen evolution reaction (HER) due to their exceptional activity, selectivity, and stability. ASCs with individual atoms dispersed on a support material, offer expanded surface areas and increased mass efficiency. This is because each atom in these catalysts serves as an active site, which enhances their catalytic activity. This review is focused on providing a detailed analysis of ASCs in the context of the HER. It will delve into their properties, types, and performance to provide a comprehensive understanding of their role in electrochemical HER processes. The introduction part underscores HER's significance in transitioning to sustainable energy sources and emphasizes the need for innovative catalysts like ASCs. The fundamentals of the HER section emphasizes the importance of understanding the HER and highlights the key role that catalysts play in HER. The review also explores the properties of ASCs with a specific emphasis on their atomic structure and categorizes the types based on their composition and structure. Within each category of ASCs, the review discusses their potential as catalysts for the HER. The performance section focuses on a thorough evaluation of ASCs in terms of their activity, selectivity, and stability in HER. The performance section assesses ASCs in terms of activity, selectivity, and stability, delving into reaction mechanisms via experimental and theoretical approaches, including density functional theory (DFT) studies. The review concludes by addressing ASC-related challenges in HER and proposing future research directions, aiming to inspire further innovation in sustainable catalysts for electrochemical HER.

Current status of developed electrocatalysts for water splitting technologies: from experimental to industrial perspective

The conversion of electricity into hydrogen (H2) gas through electrochemical water splitting using efficient electrocatalysts has been one of the most important future technologies to create vast amounts of clean and renewable energy. Low-temperature electrolyzer systems, such as proton exchange membrane water electrolyzers, alkaline water electrolyzers, and anion exchange membrane water electrolyzers are at the forefront of current technologies. Their performance, however, generally depends on electricity costs and system efficiency, which can be significantly improved by developing high-performance electrocatalysts to enhance the kinetics of both the cathodic hydrogen evolution reaction and the anodic oxygen evolution reaction. Despite numerous active research efforts in catalyst development, the performance of water electrolysis remains insufficient for commercialization. Ongoing research into innovative electrocatalysts and an understanding of the catalytic mechanisms are critical to enhancing their activity and stability for electrolyzers. This is still a focus at academic institutes/universities and industrial R&D centers. Herein, we provide an overview of the current state and future directions of electrocatalysts and water electrolyzers for electrochemical H2 production. Additionally, we describe in detail the technological framework of electrocatalysts and water electrolyzers for H2 production as utilized by relevant global companies.

Trace Ru Incorporation Boosted Co2P Nanorods for Superior Water Electrolysis and Substrate-Paired Electrolysis Toward Value-Added Chemicals in Alkaline Medium

Electro-valorization of biomass-derived chemicals has ensured sustainable production of value-added products, an effective approach for reducing carbon footprint, through renewable energy. Electrochemical oxidation and reduction reactions in aqueous media using H2O as a potential source for active hydrogenated and oxygenated species fulfill the purpose. In this study, Ru─Co2P nanorods are explored as a bifunctional electrocatalyst toward valorization of Organics at basic media. The in-situ electrogenerated Co3+ and Co4+ species act as active oxidants toward product selectivity. An overpotential of 68 mV is found for hydrogen evolution reaction (1 m NaOH) with Ru─Co2P. Further, used as cathode, Ru─Co2P effectively reduces furfuraldehyde to furfuryl alcohol and p-nitrophenol to p-aminophenol. Ru doping enables ease of formation of active species both for reduction and oxidation, faster charge transfer between catalyst to absorbates. Density Functional Theory calculation establishes Ru incorporation in Co2P surface results in enhanced adsorption of substrates. Ru doping modulates the electronic structure of Co2P which changes the density of states resulting in faster water dissociation and water splitting. To reach 10 mA cm-2 current density only 1.6 V is required for water electrolysis, whereas 1.4 V is enough for substrate-paired electrolysis with simultaneous oxidation of benzyl alcohol and reduction of p-nitro phenol.

3D NiCoW Metallic Compound Nano-Network Structure Catalytic Material for Urea Oxidation

Urea shows promise as an alternative substrate to water oxidation in electrolyzers, and replacing OER with the Urea Oxidation Reaction (UOR, theoretical potential of 0.37 V vs. RHE) can significantly increase hydrogen production efficiency. Additionally, the decomposition of urea can help reduce environmental pollution. This paper improves the inherent activity of catalytic materials through morphology and electronic modulation by incorporating tungsten (W), which accelerates electron transfer, enhances the electronic structure of neighboring atoms to create a synergistic effect, and regulates the adsorption process of active sites and intermediates. NiCoW catalytic materials with an ultra-thin nanosheet structure were prepared using an ultrasonic-assisted NaBH4 reduction method. The results show that during the OER process, NiCoW catalytic materials have a potential of only 1.53 V at a current density of 10 mA/cm2, while the UOR process under the same conditions requires a lower potential of 1.31 V, demonstrating superior catalytic performance. In a mixed electrolyte of 1 M KOH and 0.5 M urea, overall water splitting also shows excellent performance. Therefore, the designed NiCoW electrocatalyst, with its high catalytic activity, provides valuable insights for enhancing the efficiency of water electrolysis for hydrogen production and holds practical research significance.

Stability of Multivalent Ruthenium on CoWO4 Nanosheets for Improved Electrochemical Water Splitting with Alkaline Electrolyte

Engineering low-cost electrocatalysts with desired features is vital to decrease the energy consumption but challenging for superior water splitting. Herein, we development a facile strategy by the addition of multivalence ruthenium (Ru) into the CoWO4/CC system. During the synthesis process, the most of Ru3+ ions were insinuated into the lattice of CoWO4, while the residual Ru3+ ions were reduced to metallic Ru and further attached to the interface between carbon cloth and CoWO4 sheets. The optimal Ru2(M)-CoWO4/CC exhibited superior performance for the HER with an overpotential of 85 mV@10 mA cm-2, which was much better than most of reported electrocatalysts, regarding OER, a low overpotential of 240 mV@10 mA cm-2 was sufficient. In comparison to Ru2(0)-CoWO4/CC with the same Ru mass loading, multivalence Ru2(M)-CoWO4/CC required a lower overpotential for OER and HER, respectively. The Ru2(M)-CoWO4/CC couple showed excellent overall water splitting performance at a cell voltage of 1.48 V@10 mA cm-2 for used as both anodic and cathodic electrocatalysts. Results of the study showed that the electrocatalytic activity of Ru2(M)-CoWO4/CC was attributed to the in-situ transformation of Ru/Co sites, the multivalent Ru ions and the synergistic effect of different metal species stimulated the intrinsic activity of CoWO4/CC.

Tungsten doped FeCoP2 nanoparticles embedded into carbon for highly efficient oxygen evolution reaction

Designing active and stable electrocatalysts with economic efficiency for oxygen evolution reaction (OER) is essential for developing water splitting process at an industrial scale. Herein, we rationally designed a tungsten doped iron cobalt phosphide incorporated with carbon (Wx-FeCoP2/C), prepared by a mechanochemical approach. X-ray photoelectron spectroscopy (XPS) revealed that the doping of W led to an increasing of Co3+/Co2+ and Fe3+/Fe2+ molar ratios, which contributed to the enhanced OER performance. As a result, a current density of 10 mA cm-2 was achieved in 1 M KOH at an overpotential of 264 mV on the optimized W0.1-FeCoP2/C. Moreover, at high current density of 100 mA cm-2, the overpotential value was 310 mV, and the corresponding Tafel slope was measured to be 48.5 mV dec-1, placing it among the best phosphide-based catalysts for OER. This work is expected to enlighten the design strategy of highly efficient phosphide-based OER catalysts.

Flexible Bifunctional Electrode for Alkaline Water Splitting with Long-Term Stability

Progress in electrochemical water-splitting devices as future renewable and clean energy systems requires the development of electrodes composed of efficient and earth-abundant bifunctional electrocatalysts. This study reveals a novel flexible and bifunctional electrode (NiO@CNTR) by hybridizing macroscopically assembled carbon nanotube ribbons (CNTRs) and atmospheric plasma-synthesized NiO quantum dots (QDs) with varied loadings to demonstrate bifunctional electrocatalytic activity for stable and efficient overall water-splitting (OWS) applications. Comparative studies on the effect of different electrolytes, e.g., acid and alkaline, reveal a strong preference for alkaline electrolytes for the developed NiO@CNTR electrode, suggesting its bifunctionality for both HER and OER activities. Our proposed NiO@CNTR electrode demonstrates significantly enhanced overall catalytic performance in a two-electrode alkaline electrolyzer cell configuration by assembling the same electrode materials as both the anode and the cathode, with a remarkable long-standing stability retaining ∼100% of the initial current after a 100 h long OWS run, which is attributed to the "synergistic coupling" between NiO QD catalysts and the CNTR matrix. Interestingly, the developed electrode exhibits a cell potential (E10) of only 1.81 V with significantly low NiO QD loading (83 μg/cm2) compared to other catalyst loading values reported in the literature. This study demonstrates a potential class of carbon-based electrodes with single-metal-based bifunctional catalysts that opens up a cost-effective and large-scale pathway for further development of catalysts and their loading engineering suitable for alkaline-based OWS applications and green hydrogen generation.

Colloid synthesis of Ni12P5/N, S-doped graphene as efficient bifunctional catalyst for alkaline hydrogen evolution and triiodide reduction reaction

Designing high-efficient bifunction catalysts with excellent catalytic activity and enhanced charge-transfer capability in both alkaline hydrogen evolution reaction (HER) and triiodide reduction reaction (IRR) is of utmost significance to advance the development of green hydrogen production and photovoltaics, respectively, yet remains a crucial challenge. Here, highly dispersed and small-sized Ni12P5 nanocrystals with narrow size distribution was well attached on the surface of N, S co-doped graphene (Ni12P5/NSG) by the facile hot-injection method. As expected, the optimized Ni12P5/NSG requires a relatively low overpotential of 132.94 ± 0.08 mV to deliver a current density of 10 mA cm-2 in alkaline condition, accompanied with remarkable long-time durability with negligible attenuation over 50 h. Density functional theory (DFT) calculations revealed that the positively synergic effect between Ni12P5 and NSG are in favor of modulating the rate determining step of the dissociation of H2O to *(OH-H), thereby upgrading its HER activity. When used as the counter electrode catalyst for IRR in DSSCs, the resultant Ni12P5/NSG exhibits extraordinary Pt-like catalytic activity and well electrochemical stability in iodide-based electrolyte, delivering a high photoelectric conversion performance (PCE) comparable to Pt. The improved PCE can be attributed to the accelerated interfacial charge-transfer capability around active sites for facilitating the reaction kinetics of IRR, as demonstrated by DFT calculations. This work provides an effective strategy for synthesizing cost-effective composites with multi-active sites and offering valuable insight into the structure-performance relationship, which is conducive to guide the synthesis of promising catalysts in the energy conversion field.