One-step Na2S2O3-activation strategy on the construction of CoS–Co(OH)2 nanoflakes@Cu31S16 microrod architectures for alkaline overall water splitting

Research of the transition from a aqueous zinc ion battery to an aqueous hydrogen proton battery triggered by the Cu@Cu31S16 cathode material development

The aqueous zinc ion battery (AZIB) has been widely studied due to its rapid kinetics and high specific capacity attributed to the chemical insertion of H+ protons. However, the current research landscape lacks comprehensive investigations into copper-based sulfide materials and the intricate co-embedding/extraction mechanism of H+/Zn2+. In this study, we employed an innovative in-situ etching method to synthesize a current collector-integrated Cu@Cu31S16 cathode material. Cu31S16 not only exhibits excellent stability and conductivity but also activates proton insertion chemistry. Consequently, we have demonstrated, for the first time, efficient and reversible co-embedding/extraction behavior of H+/Zn2+ in Zn-Cu31S16 batteries. Specifically, owing to the lower charging and discharging plateaus of zinc ions (0.65 V, 0.45 V) compared to H+ (0.97 V, 0.84 V) in Zn-Cu31S16 batteries, two distinct plateaus were observed. Moreover, we delved into the mechanism of ion co-embedding/extraction by exploring different ions (Zn2+, H+/Zn2+, H+) within varying voltage ranges. This exploration led to the development of three types of ion batteries, where Zn2+, H+/Zn2+, and H+ exhibit co-embedding/extraction within voltage ranges of 0.3-0.9 V, 0.3-1.05 V, and 0.5-1.05 V, respectively. These batteries have achieved impressive performance with specific capacities of 282.74 mAh g-1, 587.4 mAh g-1 and 687.3 mAh g-1, respectively. Introducing the concept of "Voltage-Selective Ion Co-Embedding/Extraction", this study broadens the research scope of AZIBs. This research not only offers a feasible solution and theoretical guidance for future proton batteries but also underscores the tremendous potential of AHPB.

1D@2D Hierarchical Structures of Co(OH)x Nanosheets on NiMoOx Nanorods Can Mediate Alkaline Hydrogen Evolution with Industry-Level Current Density and Stability

Developing efficient electrocatalysts at ampere-scale current densities is of paramount importance to advance industrial applications of alkaline water electrolysis. Herein, a hierarchical nanostructured electrocatalyst with two-dimensional Co(OH)_x nanosheets grown on one-dimensional NiMoO_x nanorods over three-dimensional porous Ni foam substrate is designed. The resulting catalyst delivers ultrahigh hydrogen evolution reaction (HER) activity in the alkaline solution, which only requires overpotentials of 185 and 332 mV to achieve the current densities of -500 and -1000 mA cm^-2 in 1.0 m KOH, respectively, and shows robust stability at -1000 mA cm^-2 for 11 days. The unique 1D @ 2D hierarchical structures with abundant hetero-interfaces can not only expose sufficient active sites but also boost alkaline HER kinetics with fast water dissociation ability. This present work may pave a new insight to design efficient electrocatalysts with hierarchical structures for alkaline HER with industry-level current density and stability.

Highly Effective OER Electrocatalysts Generated from a Two-Dimensional Metal-Organic Framework Including a Sulfur-Containing Linker without Doping

Metal-organic frameworks (MOFs) with different topologies formed by the self-assembly of sulfur-containing inorganic ligands, cobalt ions, and large ligands can be used to prepare electrocatalysts for water splitting in order to fully explore the advantages of MOFs in terms of structural tailoring and quantitative assembly. It is possible to avoid using an extradoped sulfur source to reduce waste as well as to disperse Co and sulfur elements evenly and controllably throughout the final material to maximize the overall synergistic effect. In this work, different kinds of bimetallic MOF materials containing sulfur can be synthesized very conveniently by using an economical and practical diffusion method. These materials are directly used as OER electrocatalysts, and the bimetallic MOFs have the best electrocatalytic performance when the ratio of Co to Fe is 6:4. The overpotential at a current density of 10 mA cm^-2 was 260 mV, with a Tafel slope of 56 mV dec^-1 and good stability. It was assembled with 20% commercial Pt/C material into a two-electrode system for all-water decomposition, and the decomposition voltage at 10 mA cm^-2 was 1.81 V. From the electronic configuration microscopic point of view, the introduction of iron ions changed the original synergistic effect for Co-S-Co, which more easily led to the formation of high-valence Co³⁺ and finally produced highly active electrocatalytic sites. From a macroscopic point of view, the material produced in situ during the electrochemical reaction process not only retains the original 2D layered structure but also utilizes bubbles to produce a loose structure with defective sites. These structural features are advantageous because they provide not only an abundance of active sites and permeable channels but also the necessary interfaces and electron-transport channels for the formation of electrostatic charge-separation layers, making it easier to intercalate and delaminate the hydroxide ions. Furthermore, the changed hydroxyl ions and nitrogen and sulfur atoms on the channel surface may operate as interaction sites, increasing the surface characteristics, facilitating electron transfer, and reducing electron-transfer resistance. To summarize, the rational design of sulfur-containing layered MOF materials directly as water-splitting catalysts is a crucial next step in developing cost-effective, environmentally friendly, and low-energy-consumption electrocatalysts based on the findings of this study.

Chlorine-assisted synthesis of CuCo2S4@(Cu,Co)2Cl(OH)3 heterostructures with an efficient nanointerface for electrocatalytic oxygen evolution

The demand for sustainable energy sources urges the development of efficient and earth-abundant electrocatalysts. Herein, chlorine assisted ion-exchange and in-situ sulfurization processes were combined to construct CuCo₂S₄@(Cu,Co)₂Cl(OH)₃ heterostructures from Cu(OH)₂ nanoarrays. Chlorine element in the cobalt source stimulated the formation of (Cu,Co)₂Cl(OH)₃ precursor, and further facilitated partial transformation of the precursor to CuCo₂S₄ on the surface to achieve composite structure. The mixed valences of Co element (Co³⁺ in CuCo₂S₄ and Co²⁺ in (Cu,Co)₂Cl(OH)₃) and OS interpenetrated nanointerface in the composite catalysts provided low electron transfer resistance for good alkaline oxygen evolution reaction (OER) activities. In 1 mol L^-1 KOH electrolyte, the overpotentials of the optimal composite catalyst reached 253 and 290 mV respectively at the current density of 20 and 50 mA cm^-2, which is comparable to the activity of commercial Ir/C (281 mV@20 mA cm^-2). These findings could provide opportunities for designing effective and inexpensive composite electrocatalysts through nanointerface engineering strategy.