Self-supported Co9S8-Ni3S2-CNTs/NF electrode with superwetting multistage micro-nano structure for efficient bifunctional overall water splitting

One-Step Electrodeposition of Ternary Metal Sulfide Composite Nanorod Arrays as a Self-Supported Electrocatalyst for the Hydrogen Evolution Reaction

In this study, a self-supported material with a unique ternary metal sulfide nanorod array structure was fabricated in situ on copper foam via a facile one-step electrodeposition approach ((NiCo-Cu)Sx/CF). The electrochemically driven rapid generation of abundant S2- ions from thiourea accelerates their combination with Ni2+ and Co2+, resulting in a catalytically enriched surface on the nanorod array. The high-density nanorod arrays provide maximally accessible active sites, thereby enhancing the hydrogen evolution reaction (HER). The in situ grown self-supported structure effectively eliminates the need for binders (common in conventional catalysts), avoids additional interfacial resistance, and ensures long-term stability during electrocatalytic operation. The synergistic interactions among the metal components (Ni, Co, and Cu) optimize the local electronic environment, creating favorable conditions for catalytic hydrogen evolution. The experimental results demonstrate that the ternary metal sulfide nanocomposite (denoted as (NiCo-Cu)Sx/CF) exhibits superior hydrogen evolution reaction performance compared to its binary counterparts. Remarkably, the catalyst required only 42 and 161 mV overpotential to deliver 10 mA·cm-2 and 100 mA·cm-2 current densities in 1 M KOH, respectively, with 100 h operational stability. This work provides a viable strategy for developing self-supported ternary non-noble metal catalysts for energy conversion applications.

MOF-Derived Ni5P4 Nanoparticles Based on the Microemulsion Strategy for Supercapacitors and Water Splitting

With the rapid advancement of energy storage and conversion systems (ESCSs), renewable energy can achieve a smooth and continuous output capacity. Nevertheless, commercial precious metal-based multifunctional ESCSs materials are plagued by issues like scarcity and high production costs. This study adopted microemulsion and chemical vapor deposition (CVD) strategies to fabricate single crystal Ni5P4 nanoparticles successfully. Due to its excellent crystal integrity and high electrical conductivity, single crystal Ni5P4 offers abundant active sites for redox reactions. Additionally, it allows electrons and ions to move more efficiently and freely, making it a highly promising multifunctional material for ESCSs. For supercapacitors (SCs), the prepared Ni5P4-10 electrode possesses a battery-like behavior with a high specific capacity of 1643.13 F g-1@0.5 A g-1. The corresponding assembled Ni5P4-10//AC hybrid SCs (HSCs) exhibit a maximum energy density of 37.78 Wh kg-1 at a power density of 400 W kg-1. Furthermore, Ni5P4-10 displays low overpotentials of 150 mV@HER and 250 mV@OER at 10 mA cm-2 when it serves as an electrocatalyst. This study offers a novel perspective for the design of MOF-derived multifunctional ESCSs materials.

Amorphous/crystalline nanostructured Co-FeOOH/CoCe-MOF/NF heterojunctions for efficient electrocatalytic overall water splitting

Hydrogen production by electrocatalytic water splitting is considered to be an effective and environmental method, and the design of an electrocatalyst with high efficiency, low cost, and multifunction is of great importance. Herein, we developed a amorphous Co-FeOOH/crystalline CoCe-MOF heterostructure (defined as Co-FeOOH/CoCe-MOF/NF) though a convenient cathodic electrodeposition strategy as a high-efficiency bifunctional electrocatalyst for water electrolysis. The Co-FeOOH/CoCe-MOF/NF nanocrystals provide remarkable electronic conductivity and plenty of active sites, and the crystalline/amorphous heterostructure with generates synergistic effects, providing plentiful active sites and efficient charge/mass transfer. Benefiting from this, the designed Co-FeOOH/CoCe-MOF/NF displays ultralow overpotentials of 226 and 74 mV to achieve 10 mA cm-2 for oxygen evolution reaction and hydrogen evolution reaction, and also shows the superior performance for overall water splitting with a low voltage of 1.55 V at 10 mA cm-2 in 1 M KOH. The work reveals a design of superior activity, cost-effective and multifunctional electrocatalysts for water splitting.

Improved HER/OER Performance of NiS2/MoS2 Composite Modified by CeO2 and LDH

In recent years, there has been significant interest in transition-metal sulfides (TMSs) due to their economic affordability and excellent catalytic activity. Nevertheless, it is difficult for TMSs to achieve satisfactory performance due to problems such as low conductivity, limited catalytic activity, and inadequate stability. Therefore, a catalyst with a heterostructure constituted of a nickel-iron-layered double hydroxide, nickel sulfide, molybdenum disulfide, and cerium dioxide was designed. At the current density of 10 mA cm-2 in an alkaline solution, the catalyst exhibits a HER overpotential of 116 mV. In addition, an overpotential of 235 mV@150 mA cm-2 was displayed for OER. The catalyst showed a good retention rate (94.7% for HER, 98.6% for OER) after 160 h stability tests. The excellent electrochemical performance is attributed to the following points: 1. The self-supporting three-dimensional hierarchical structure provides abundant sites, fast ion diffusion channels, and electron transfer paths, and ensures structural stability. 2. The strong interfacial electron interaction between Ni3S2/MoS2 heterojunction and NiFe-LDH improves the OER reaction kinetics. 3. The Ce3+ and oxygen vacancies in CeO2 promote the dissociation of H2O and promote the HER reaction kinetics. This approach paves the way for developing highly efficient electrocatalysts for various electrochemical applications.

Phosphorus/sulfur co-doped heterogeneous NiCoPxSy nanoarrays boosting overall water splitting

In the large-scale implementation of renewable energy devices, the availability of stable and highly catalytic non-precious metal catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial. Meanwhile, integrating bifunctional electrocatalysts simultaneously on both the anode and cathode still faces challenges. To address this, a stepped preparation strategy was adopted on a nickel foam (NF) substrate to synthesize P, S co-doped NiCoPxSy nanowire array catalysts. The prepared NiCoPxSy catalysts demonstrated a small Tafel slope of 72.5 mV dec-1 for HER and 72.3 mV dec-1 for OER by requiring only 37 mV (326 mV) overpotential to achieve a current density of 10 mA cm-2 (50 mA cm-2). Moreover, when assembled into an electrolytic cell in 1 M KOH, the NiCoPxSy catalysts achieved a low voltage of 1.55 V at 10 mA cm-2 current density and exhibited long-term stability. The outstanding electrocatalytic performance can be attributed to the influence of doped anions on the electronic states and distribution among different atoms, which thereby positively affected the electrocatalytic activity. This research provides an effective method for designing innovative catalysts and paving the way to produce clean energy.

Flower ball cathode assembled from Cu doped Co3S4/Ni3S2 ultrathin nanosheets in a photocatalytic fuel cell for efficient photoelectrochemical rifampicin purification and simultaneous electricity generation based on a CuO QDs/TiO2/WO3 photoanode

Herein, an efficient CuO QDs/TiO₂/WO₃ photoanode and a Cu doped Co₃S₄/Ni₃S₂ cathode were successfully synthesized. The optimized CuO QDs/TiO₂/WO₃ photoanode achieved a photocurrent density of 1.93 mA cm^-2 at 1.23 vs. RHE, which was 2.27 times that of a WO₃ photoanode. The CuO QDs/TiO₂/WO₃-buried junction silicon (BJS) photoanode was coupled with the Cu doped Co₃S₄/Ni₃S₂ cathode to construct a novel photocatalytic fuel cell (PFC) system. The as-established PFC system showed a high rifampicin (RFP) removal ratio of 93.4% after 90 min and maximum power output of 0.50 mW cm^-2. Quenching tests and EPR spectra demonstrated that ˙OH, ˙O₂^- and ¹O₂ were the main reactive oxygen species in the system. This work provides a possibility to construct a more efficient PFC system for environmental protection and energy recovery in the future.

A salt-baking 'recipe' of commercial nickel-molybdenum alloy foam for oxygen evolution catalysis in water splitting

Ni-based metal foam holds promise as an electrochemical water-splitting catalyst, due to its low cost, acceptable catalytic activity and superior stability. However, its catalytic activity must be improved before it can be used as an energy-saving catalyst. Here, a traditional Chinese recipe, salt-baking, was employed to surface engineering of nickel-molybdenum alloy (NiMo) foam. During salt-baking, a thin layer of FeOOH nano-flowers was assembled on the NiMo foam surface then the resultant NiMo-Fe catalytic material was evaluated for its ability to support oxygen evolution reaction (OER) activity. The NiMo-Fe foam catalyst generated an electric current density of 100 mA cm^-2 that required an overpotential of only 280 mV, thus demonstrating that its performance far exceeded that of the benchmark catalyst RuO₂ (375 mV). When employed as both the anode and cathode for use in alkaline water electrolysis, the NiMo-Fe foam generated a current density (j) output that was 3.5 times greater than that of NiMo. Thus, our proposed salt-baking method is a promising simple and environmentally friendly approach for surface engineering of metal foam for designing catalysts.