Interfacial Engineering of Copper-Nickel Selenide Nanodendrites for Enhanced Overall Water Splitting in Alkali Condition

Dual chalcogenide coordination engineering on a self-supported alloy electrode for enhanced hydrogen evolution reaction

The electrochemical hydrogen evolution reaction (HER) holds substantial promise for large-scale green hydrogen production due to its cost-effectiveness, high performance, and scalability for repeated implementation. A promising strategy that involves a novel transition-metal chalcogenide with a self-supported framework can improve the reaction kinetics in the HER. We synthesize a nano three-dimensional self-supported HER catalyst via a straightforward one-step chemical vapor deposition process. This method incorporates a dual co-reaction with sulfur (S) and selenium (Se) onto a commercially available Monel alloy (CNSSe). The dynamics ion exchange redox reactions promote the formation of heterogeneous catalyst structures. Density functional theory (DFT) calculations indicate that the CNSSe catalyst exhibits low hydrogen coverage, as evidenced by a thermoneutral free energy of adsorbed hydrogen (ΔGH*) of 0.105 eV, which can be attributed to the dual introduction of S and Se. Consequently, the optimized CNSSe electrocatalyst achieves an enhancement in HER performance exceeding 100% compared to catalysts introduced exclusively with either S or Se. These results underscore the substantial potential of the optimized CNSSe electrocatalyst to improve both the performance and economic feasibility of HER technologies in alkaline water electrolysis.

Synergistic Configuration of Binary Rhodium Single Atoms in Carbon Nanofibers for High-Performance Alkaline Water Electrolyzer

Electrochemical alkaline water electrolysis offers significant economic advantages; however, these benefits are hindered by the high kinetic energy barrier of the water dissociation step and the sluggish kinetics of the hydrogen evolution reaction (HER) in alkaline media. Herein, the ensemble effect of binary types of Rh single atoms (Rh-Nx and Rh-Ox) on TiO2-embedded carbon nanofiber (Rh-TiO2/CNF) is reported, which serves as potent active sites for high-performance HER in anion exchange membrane water electrolyzer (AEMWE). Density functional theory (DFT) analyses support the experimental observations, highlighting the critical role of binary types of Rh single atoms facilitated by the TiO2 sites. The Rh-TiO2/CNF demonstrates an impressive areal current density of 1 A cm-2, maintaining extended durability for up to 225 h in a single-cell setup. Furthermore, a 2-cell AEMWE stack utilizing Rh-TiO2/CNF is tested under industrial-scale conditions. This research makes a significant contribution to the commercialization of next-generation high-performance and durable AEMWE stacks for clean hydrogen production.

Se-Doped CoS2@MoS2 Heterostructures on Multiwalled Carbon Nanotubes as Efficient Bifunctional Electrocatalysts for Alkaline Overall Water Splitting

The use of efficient and affordable non-precious metal catalysts for hydrogen and oxygen evolution reactions is vital for replacing and widely implementing new energy sources. Nevertheless, improving the catalytic performance of these non-precious-metal bifunctional electrocatalysts continues to be a major challenge. In this article, an optimized Se-incorporated bulk CoS2@MoS2 heterostructure grown on the surface of carbon nanotubes is reported. The resulting Se-CoS2@MoS2/CNTs exhibit robust bifunctional electrocatalytic performance, with low overpotentials of 85 and 240 mV @ 10 mA·cm-2 for HER and OER, respectively. The materials exhibit superior long-term stability of over 145 h, surpassing most electrocatalysts of similar type. This enhanced performance is attributed to the synergistic effect at the interface between the MoS2 and CoS2 phases, abundant active sites, and high active surface area, which collectively improves the electron-transfer efficiency during the reaction process. Furthermore, the incorporation of the amorphous state of Se into the heterostructure yields a change in the crystallinity of the heterostructure in the electronic structure, which optimizes the adsorption and activation energy barriers of the catalytic intermediate. This study thus presents a promising approach to regulating anion doping in bifunctional electrocatalysts.

MOF-Derived Co(Fe)OOH Slab and Co/MoN Nanosheet-Covered Hollow-Slab for Efficient Overall Water Splitting

The development of economical, efficient, and stable nonprecious metal electrocatalysts presents a crucial approach to achieving alkaline overall water splitting and generating renewable hydrogen. This work presents a simple method for the synthesis of transition metal oxyhydroxides and nitrides derived from the MOF template with different morphological structures for efficient overall water splitting. Co(Fe)OOH slab array is obtained by the electro-activation of Fe-doped Co-MOF precursor, which is usually regarded as the real active substance in the alkaline OER process. Doping the Co(Fe)OOH with Fe alters the local electronic structure of the Co sites, leading to a notable improvement in OER performance, which shows an overpotential of 209 mV at 10 mA cm-2 and demonstrates excellent stability. On the other hand, Co/MoN nanosheet-covered hollow-slab heterostructure is prepared by the nitrogenization of Na2MoO4-etched Co-MOF template, which displays superior HER performance due to its abundant electrochemical active sites and rapid interfacial electron transfer, achieving an overpotential of 37 mV at 10 mA cm-2 while sustaining good stability. Notably, utilizing Co(Fe)OOH as the anode and Co/MoN as the cathode in the alkaline electrolyzer results in a cell voltage of 1.49 V at 10 mA cm-2, while demonstrating a remarkable long-term stability of 100 h. This work provides a facile way to construct an efficient alkaline electrolyzer for overall water splitting by controlling the structures of MOF derivatives.

Interfacial coupling of NiSe in heterostructures promotes electrocatalytic hydrolysis of MoS2

Molybdenum sulfide (MoS2) has attracted much attention as a potential catalyst for the oxygen evolution reaction (OER), but its unique low activity and low edge active centers limit its electrocatalytic activity. In this study, catalysts were prepared by growing NiSe nanoclusters in situ onto MoS2 substrates via electrodeposition; ultrathin MoS2 nanosheets and NiSe nanoclusters were cross-linked with each other to form a unique three-dimensional rosette structure; and MoS2@NiSe catalysts were successfully synthesised, which significantly improved bifunctional catalytic performance. The synthesised MoS2@NiSe catalysts exhibited good electrochemical performance: overpotentials required to satisfy the HER and OER processes at a current density of 10 mA cm-2 in 1 M KOH were 80 mV and 254 mV, respectively. When applied as a cathode and anode to assemble a bifunctional electrode system, the MoS2@NiSe||MoS2@NiSe electrolytic cell system required only 1.54 V to achieve 10 mA cm-2 in an alkaline electrolyte, which exceeded the value of most of the bifunctional catalysts reported in the literature to date. In addition, the catalyst maintained good surface structure and catalytic performance after a 24 h stability test. This study provides a new idea for the improvement and design of MoS2-based bifunctional catalysts and provides an important reference for research in the field of clean energy.

Influence of deposition conditions on performance of Ni3S2 as the bifunctional electrocatalyst in alkaline solutions by galvanostatic deposition

The electrodeposition method is a popular synthesis method due to its low cost, simplicity, and short synthesis time. In addition, this synthesis route results in the preparation of a self-supporting electrocatalyst, which eliminates the use of binders and ultimately facilitates the durability as well as the activity of the catalyst. In this work, a series of Ni3S2/Ni mesh electrodes are prepared by galvanostatic deposition at different deposition current densities and times. The morphology, microstructure, and elemental composition distribution of these obtained electrodes are characterized, and the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance of the series of Ni3S2/Ni meshes are tested. The results show that the Ni3S2/Ni mesh electrodes electrodeposited at 30 mA cm-2 for 1200 s have superior electrochemical performance for HER and OER. The overpotentials of Ni3S2/Ni mesh 30 mA cm-2-1200 s are 236 and 244 mV for HER and OER, respectively, at a current density of 10 mA cm-2. In addition, the Tafel slopes for HER and OER are 113 mV dec-1 and 176 mV dec-1, respectively. This research provides some valuable insights into the use of the electrodeposition method for the fabrication of electrocatalysts.

Interface Enables Faster Surface Reconstruction in a Heterostructured CuSey/NiSex Electrocatalyst for Realizing Urea Oxidation

Creating affordable electrocatalysts and understanding the real-time catalytic process of the urea oxidation reaction (UOR) are crucial for advancing urea-based technologies. Herein, a Cu-Ni based selenide electrocatalyst (CuSey/NiSex/NF) was created using a hydrothermal technique and selenization treatment, featuring a heterogeneous interface rich in Cu2-xSe, Cu3Se2, Ni3Se4, and NiSe2. This catalyst demonstrated outstanding urea electrooxidation performance, achieving 10 mA cm-2 with just 1.31 V and sustaining stability for 96 h. Through in-situ Raman spectroscopy and ex-situ characterizations, it is discovered that NiOOH is formed through surface reconstruction in the UOR process, with high-valence Ni serving as the key site for effective urea oxidation. Moreover, the electrochemical analysis revealed that CuSey had dual effects. An analysis of XPS and electrochemical tests revealed that electron transfer from CuSey to NiSex within the CuSey/NiSex/NF heterostructure enhanced the UOR kinetics of the catalyst. Additionally, according to the in-situ Raman spectroscopy findings, the existence of CuSey facilitates a easier and faster surface reconstruction of NiSex, leading to the creation of additional active sites for urea oxidation. More significantly, this work provides an excellent "precatalyst" for highly efficient UOR, along with an in-depth understanding of the mechanism behind the structural changes in electrocatalysts and the discovery of their true active sites.

SOx Functionalized NiOOH Nanosheets Embedded in Ni(OH)2 Microarray for High-Efficiency Seawater Oxidation

A nano-micro heterostructure has been established to address the challenges of selectivity, stress, pitting corrosion, and long-term durability of anodes in unpurified seawater. The heterostructure comprised NiOOH nanosheets embedded within a high surface area Ni(OH)2 microarray, and the surface structure is further functionalized with sulfate (SOx). This cation-selective protective layer impedes chloride (Cl-) diffusion and abstracts H from reaction intermediates, leading to enhanced selectivity and corrosion resistance of the anode. The multilevel porosity within the randomly oriented nanosheets and the underlying support provide short diffusion channels for ions and mass migration, ensuring efficient ion transport and long-term structural and mechanical durability of the active sites, even at high current density. Remarkably, the catalyst requires a small input voltage of 400 mV to deliver a current density of 1 A cm-2 and maintains it for over 168 h without noticeable degradation or hypochlorite formation. Spectroscopic analysis and density functional theory (DFT) calculations reveal that the Ni electronic structure in the +3 valence state, its strong structural interaction with the underlying microarray, and the functionality of SOx significantly reduce the required potential for O-O coupling.

Interfacial Interaction in NiFe LDH/NiS2/VS2 for Enhanced Electrocatalytic Water Splitting

A bifunctional electrocatalyst with high efficiency and low costs for overall water splitting is critical to achieving a green hydrogen economy and coping with the energy crisis. However, developing robust electrocatalysts still faces huge challenges, owing to unsatisfactory electron transfer and inherent activity. Herein, NiFe LDH/NiS2/VS2 heterojunctions have been designed as freestanding bifunctional electrocatalysts to split water, exhibiting enhanced electron transfer and abundant catalytic sites. The optimum NiFe LDH/NiS2/VS2 electrocatalyst exhibits a small overpotential of 380 mV at 10 mA cm-2 for overall water splitting and superior electrocatalytic performance in both hydrogen and oxygen evolution reactions (HER/OER). Specifically, the electrocatalyst requires overpotentials of 76 and 286 mV at 10 mA cm-2 for HER and OER, respectively, in alkaline electrolytes, which originate from the synergistic interaction among the facilitated electron transfer and increasingly exposed active sites due to the modulation of interfaces and construction of heterojunctions.

Tuning the interface of MIMII(OH)F@MIMII1-xS (MⅠ: Ni, Co; MⅡ: Co, Fe) by atomic replacement strategy toward high performance overall water splitting

Constructing heterostructure is considered as one of the most promising strategies to reveal high efficiency hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance. Nevertheless, it is highly challenging to obtain stable interfaces and sufficient active sites via conventional method. In addition, Ni, Co and Fe elements share the valence electron structures of 3d6-84s2, the appropriate integration of these metals to induce synergistic effect in multicomponent electrocatalysts can enhance electrochemical activity. Herein, in this work, the MIMII(OH)F@MIMII1-xS (NiFe(OH)F@NiFe1-xS, NiCo(OH)F@NiCo1-xS, CoFe(OH)F@CoFe1-xS) autogenous heterostructure on nickel foam are constructed. As a result, NiFe(OH)F@NiFe1-xS-0.05, NiCo(OH)F@NiCo1-xS-0.05, and CoFe(OH)F@CoFe1-xS-0.05 demonstrate outstanding overpotential for HER (70 mV, 90 mV, 81 mV at -10 mA cm-2) and OER (370 mV, 470 mV, 370 mV at 10 mA cm-2) in alkaline electrolyte, while the overpotential for HER is 176 mV, 189 mV, 167 mV at -10 mA cm-2 and corresponding OER is 290 mV, 390 mV, 300 mV at 10 mA cm-2 in simulated seawater, respectively. In addition, the NiFe, NiCo, CoFe-based electrolyzer acquire favorable overall water splitting activity in alkaline (1.72 V, 1.87 V, 1.66 V) and simulated seawater (1.73 V, 1.75 V, 1.69 V) at 10 mA cm-2. Overall, the above results authenticate the feasibility of developing autogenous heterostructure electrocatalysts for providing hydrogen and oxygen in alkaline and simulated seawater.

Triple roles of Ni(OH)2 promoting the electrocatalytic activity and stability of Ni3S4@Ni(OH)2 in anion exchange membrane water electrolyzers

Developing high performance and durable electrocatalysts is crucial for the practical application of large-scale water splitting under high current density. Here, we constructed a Mott-Schottky heterojunction bifunctional electrocatalyst coating of Ni3S4 with Ni(OH)2 thin film supported on Ni foam substrate (Ni3S4@Ni(OH)2) for anion exchange membrane water electrolyzers (AEMWEs). Remarkably, the η500 is as low as 274.6 mV toward the hydrogen evolution reaction and 423.8 mV toward the oxygen evolution reaction. AEMWEs deliver a stable performance that achieves current densities of 500 and 1000 mA cm-2 at a cell voltage of 1.84 and 1.95 V, respectively. In particular, the Ni3S4@Ni(OH)2 exhibits durable stability for 100 h at 500 mA cm-2 without significant degradation and uses 0.75 kW·h of electricity less than commercial Ni foam electrode to produce each standard cubic meter of hydrogen gas at 500 mA cm-2. The excellent performance is ascribed to the triple roles of Ni(OH)2, which prevent the inner Ni3S4 from decomposing during the reaction process, promoting the dissociation of water and formation of adsorbed hydrogen intermediate and accelerating electron transfer ability due to the Mott-Schottky heterojunction between Ni(OH)2 and Ni3S4. This work sheds light on the development of advanced bifunctional electrocatalysts based on non-precious transition metals for AEMWEs.

Fabricating Ru Atom-Doped Novel FeP4/Fe2PO5 Heterogeneous Interface for Overall Water Splitting in Alkaline Environment

Developing bifunctional electrocatalysts with low-content noble metals and high activity and stability is crucial for water splitting. Herein, we reported a novel Ru doped FeP4/Fe2PO5 heterogeneous interface catalyst (Ru@FeP4/Fe2PO5) for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) by heat treatment coupling electrodeposition strategy. Experiments disclosed that Ru@FeP4/Fe2PO5 proclaimed excellent catalytic activity for the OER (249 mV@100 mA cm-2) and HER (49 mV@10 mA cm-2) in a 1 M KOH environment. More importantly, the mass activity and turnover frequency of Ru@FeP4/Fe2PO5 were 117 and 108 times higher than that of commercial RuO2 at an overpotential of 300 mV during the OER, respectively. In addition, the assembled Ru@FeP4/Fe2PO5 || Ru@FeP4/Fe2PO5 system could retain superior durability in a two-electrode system for 134 h at 300 mA cm-2. Further mechanism studies revealed that Ru atoms in Ru@FeP4/Fe2PO5 act in a key role for the excellent activity during water splitting because the electronic structure of Ru sites could be optimized by the interaction between Ru and Fe atoms at the interface to strengthen the adsorption of reaction intermediates. Besides, the introduction of Ru atoms could also enhance the charge transfer, which effectually accelerates the reaction kinetics. The strategy of anchoring Ru atom on novel heterostructure provides a promising path to boost the overall activity of electrocatalysts for water splitting.