Integration of ZnCo2S4 nanowires arrays with NiFe-LDH nanosheet as water dissociation promoter for enhanced electrocatalytic hydrogen evolution

Two birds with one stone: Bimetallic ZnCo2S4 polyhedral nanoparticles decorated porous N-doped carbon nanofiber membranes for free-standing flexible anodes and microwave absorption

Cost-efficient material with an ingenious design is important in the engineering applications of flexible energy storage and electromagnetic (EM) protection. In this study, bimetallic ZnCo2S4 (ZCS) polyhedral nanoparticles homogenously embedded in the surface of porous N-doped carbon nanofiber membranes (ZCS@PCNFM) have been fabricated by electrospinning technique combined with carbonization and hydrothermal processes. As a self-assembled electrode for lithium-ion batteries (LIBs), the bimetallic ZCS nanoparticles possess rich redox reactions, good electrical conductivity, and pseudocapacitive properties, while the three-dimensional (3D) multiaperture architecture of the nanofiber film not only shortens the transfer spacing of lithium ions and electrons but also effectively tolerates the volume variation during lithiation and delithiation cycles. Benefiting from the above merits, the ZCS@PCNFM electrode exhibits good cycle performance (662.3 mA h/g at 100 mA/g after 100 cycles), superior rate capacity (401.3 mA h/g at 1 A/g) and an extremely high initial specific capacity of 1152.2 mAh/g at 100 mA/g. Meanwhile, depending on the hierarchical nanostructure and multi-component heterogeneous interface effects constructed by 3D inlaid architecture, the ZCS@PCNFM nanocomposite exhibits fascinating microwave absorption (MA) characteristics with a superhigh reflection loss (RL) of -49.7 dB at a filling content of only 20 wt% and corresponding effective absorption bandwidth (EAB, RL<-10 dB) of 5.2 GHz ranging from 12.8 to 18.0 GHz at 2.2 mm.

Template free-synthesis of cobalt-iron chalcogenides [Co0.8Fe0.2L2, L = S, Se] and their robust bifunctional electrocatalysis for the water splitting reaction and Cr(vi) reduction

The ease of production of materials and showing multiple applications are appealing in this modern era of advanced technology. This paper reports the synthesis of a pair of novel cobalt-iron chalcogenides [Co0.8Fe0.2S2 and Co0.8Fe0.2Se2] with enhanced electro catalytic activities. These ternary metal chalcogenides were synthesized by a one-step template-free approach via a hexamethyldisilazane (HMDS)-assisted synthetic method. Transient photocurrent (TPC) studies and electrochemical impedance spectra (EIS) of these materials showed free electron mobility. Their bifunctional activities were verified in both the electrochemical oxygen evolution reaction (OER) and in the electrochemical reduction of toxic inorganic heavy metal ions [Cr(vi)] in polluted water. The materials showed robust catalytic ability in the oxygen evolution reaction with minimum possible over potential (345 and 350 mV @ η10) as determined by linear sweep voltammetry and the lower Tafel values (52.4 and 84.5 mV dec-1) for Co0.8Fe0.2Se2 and Co0.8Fe0.2S2 respectively. Surprisingly, both the materials also showed an excellent activity towards electrochemical Cr(vi) reduction to Cr(iii). Besides the maximum current achieved for Co0.8Fe0.2S2, a minimum value for the Limit of detection (LOD) was obtained for Co0.8Fe0.2S2 (0.159 μg L-1) compared to Co0.8Fe0.2Se2 (0.196 μg L-1). We tested the durability of catalysts, the critical factor for the prolonged use of catalysts, through the recyclability measurements of these materials as catalysts. Both the catalysts presented outstanding durability and balanced electro catalytic activities for up to 1500 CV cycles, and chronoamperometry studies also confirmed exceptional stability. The enhanced catalytic activities of these materials are ascribed to the free electron movement, evidenced by the increased TPC measured and EIS. Therefore, the template-free synthesis of these electro catalysts containing non-noble metal illustrates the practical approach to develop such types of catalysts for multiple functions.

Phosphorus doped nickel selenide for full device water splitting

The lack of high active and stable electrocatalysts has impeded the development of electrochemical water splitting device, which is promising technique for renewable energy conversion system. Here, we report a one-step protocol to synthesize P doped NiSe₂ (P-NiSe₂) by selenylation process derived from nickel foam with assistant of NaH₂PO₂ and Se powder. The P-NiSe₂ could be directly used as working electrode and shows the superior electrochemical activity, offering current density of 10 mA cm^-2 with overpotential of 270 mV for OER and 71 mV for HER. The enhanced electrochemical activity can be ascribed to the P atom doping. The P atom doping leads to the high valence state of Ni active sites, which have high catalytic ability towards OER. Moreover, the P doping makes the d-band center of Ni atoms in P-NiSe₂ move close to Fermi level, facilitating the HER kinetics with respect to proton adsorption and hydrogen desorption. When employed P-NiSe₂ as both anodic and cathodic electrode in alkaline water electrolyzer, a current density of 10 mA cm^-2 can be achieved at 1.58 V. Our work highlights the importance of P doping in determining the surface electron configuration for full device water splitting and the facile synthesis protocol would be promising for realistic applications.

Self-supported nickel sulfide derived from nickel foam for hydrogen evolution and oxygen evolution reaction: effect of crystal phase switching

Designing and fabricating economically viable, high active and stable electrocatalysts play an important role for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Crystal phase is the crucial factor that governs the electrochemical property and electrocatalytic reaction pathways. Here, a one-step nickel foam derived sulfidation method was presented to synthesize self-supported NiS₂ and Ni₃S₂. The crystal phase-dependent chemical properties related to electrocatalytic behavior were evaluated by a series of advanced characterization and density functional theory calculations. Overall, the self-supported Ni₃S₂ shows high electrochemical activity towards both HER and OER in alkaline conditions, which afford the current density of 10 mA cm^-2 with overpotentials of 245 mV for OER and 123 mV for HER, respectively. When employed the self-supported Ni₃S₂ as the bifunctional electrocatalysts for overall water splitting, the entire device provides the current density of 10 mA cm^-2 at 1.61 V. These results indicate that the electrocatalytic properties can be exert greater improved by controlling the crystal phase, offering the prospect for advanced materials design and development.

Synergistically coupling of Fe-doped CoP nanocubes with CoP nanosheet arrays towards enhanced and robust oxygen evolution electrocatalysis

The rational design of high-performance and low-cost oxygen evolution reaction (OER) electrocatalysts for water splitting is of vital importance for development of renewable hydrogen energy. Herein, we demonstrate an interfacial engineering strategy to prepare Fe-doped CoP nanocubes/CoP nanosheet arrays heterostructure supported on carbon cloth (denoted as CoFeP/CoP/CC). The resultant CoFeP/CoP/CC heterostructure catalyst possesses abundant heterogeneous interfaces, which enables the exposure of reaction active sites and possibly modulation of electronic structure of the catalyst. Furthermore, this strong interfacial coupling of CoFeP and CoP as well as the integration structure on the carbon cloth guarantee high electronic conductivity and enhanced mechanical stability. Benefiting from these advantages, the CoFeP/CoP/CC-heterostructure exhibits high electrocatalytic OER performance with a low overpotential of 240 mV for reaching a current density of 10 mA cm^-2, which outperforms the commercial noble metal RuO₂ (255 mV) and many reported TMPs-based electrocatalysts. Moreover, this CoFeP/CoP/CC catalyst shows a remarkable OER catalytic stability over 100 h. This work provides an effective avenue for the design of the high-performance OER catalyst by interfacial engineering strategy.

Core-shell nanostructured electrocatalysts for water splitting

As the cornerstone of the hydrogen economy, water electrolysis consisting of the hydrogen and oxygen evolution reactions (HER and OER) greatly needs cost-efficient electrocatalysts that can decrease the dynamic overpotential and save on energy consumption. Over past years, observable progress has been made by constructing core-shell structures free from or with few noble-metals. They afford particular merits, e.g., a highly-exposed active surface, modulated electronic configurations, strain effects, interfacial synergy, or reinforced stability, to promote the kinetics and electrocatalytic performance of the HER, OER and overall water splitting. So far, a large variety of inorganics (carbon and transition-metal related components) have been introduced into core-shell electrocatalysts. Herein, representative efforts and progress are summarized with a clear classification of core and shell components, to access comprehensive insights into electrochemical processes that proceed on surfaces or interfaces. Finally, a perspective on the future development of core-shell electrocatalysts is offered. The overall aim is to shed some light on the exploration of emerging materials for energy conversion and storage.

A three-dimensional porous CoSnS@CNT nanoarchitecture as a highly efficient bifunctional catalyst for boosted OER performance and photocatalytic degradation

It is urgent and significant to develop competent, inexpensive transition metal-based catalysts with multifunctional catalytic properties for wide applications. To meet this requirement, herein, for the first time, we present a novel bifunctional CoSnS@CNT hybrid via a simple one-pot surfactant-free hydrothermal method. The CoSnS@CNT hybrid has a unique three-dimensional (3D) porous nanoarchitecture, which is constructed by ultrathin CoSnS homogenously and compactly anchored on a highly conductive CNT skeleton. The porous nanoarchitecture of CoSnS@CNT provides abundant catalytic sites and facilitates ion diffusion, and the CNT skeleton accelerates electron transfer. Benefitting from these merits, the CoSnS@CNT hybrid acted as a bifunctional catalyst with boosted electrocatalytic and photocatalytic performance, where it delivered a tremendous oxygen evolution reaction (OER) performance with a low overpotential of 330 mV at a current density of 10 mA cm^-2 and excellent outstanding stability. Moreover, it showed 91.72% photocatalytic degradation for Rhodamine B dye, which is 2-times higher than that of bare CoSnS. This study presents a systematic approach to judiciously design nanostructures and simply synthesize non-noble metal-based bifunctional catalysts with boosted electrocatalytic and photocatalytic activities.