Endogenous Interfacial Mo-C/N-Mo-S Bonding Regulates the Active Mo Sites for Maximized Li+ Storage Areal Capacity.

Active sites, mass loading, and Li-ion diffusion coefficient are the benchmarks for boosting the areal capacity and storage capability of electrode materials for lithium-ion batteries. However, simultaneously modulating these criteria to achieve high areal capacity in LIBs remains challenging. Herein, MoS2 is considered as a suitable electroactive host material for reversible Li-ion storage and establish an endogenous multi-heterojunction strategy with interfacial Mo-C/N-Mo-S coordination bonding that enables the concurrent regulation of these benchmarks. This strategy involves architecting 3D integrated conductive nanostructured frameworks composed of Mo2 C-MoN@MoS2 on carbon cloth (denoted as C/MMMS) and refining the sluggish kinetics in the MoS2 -based anodes. Benefiting from the rich hetero-interface active sites, optimized Li adsorption energy, and low diffusion barrier, C/MMMS reaches a mass loading of 12.11 mg cm-2 and showcases high areal capacity and remarkable rate capability of 9.6 mAh cm-2 @0.4 mA cm-2 and 2.7 mAh cm-2 @6.0 mA cm-2 , respectively, alongside excellent stability after 500 electrochemical cycles. Moreover, this work not only affirms the outstanding performance of the optimized C/MMMS as an anode material for supercapacitors, underscoring its bifunctionality but also offers valuable insight into developing endogenous transition metal compound electrodes with high mass loading for the next-generation high areal capacity energy storage devices.

Bi-cation incorporated Ni3N nanosheets boost water dissociation kinetics for enhanced alkaline hydrogen evolution activity.

Nickel nitride (Ni3N) is a promising electrocatalyst for the hydrogen evolution reaction (HER) owing to its excellent metallic features and has been demonstrated to exhibit considerable activity for water oxidation. However, its undesirable characteristics as an HER electrocatalyst due to its poor unfavourable d-band energy level significantly limit its water dissociation kinetics. Herein, the HER electrocatalytic activity of Ni3N was prominently enhanced via the simultaneous incorporation of bi-cations (vanadium (V) and iron (Fe), denoted as V-Fe-Ni3N). The optimized V-Fe-Ni3N displays impressive performance with an overpotential of 69 mV at 10 mA cm-2 and good stability in 1.0 M KOH, which is remarkably better than pristine Ni3N, V-doped Ni3N, and Fe-doped Ni3N and considerably closer to a commercial Pt/C catalyst. Based on density functional theory (DFT) studies, V and Fe atoms not only serve as active sites for promoting water dissociation kinetics but also tune the electronic structure of Ni3N to achieve optimized hydrogen adsorption capabilities. This work presents an inclusive understanding of the rational designing of high-performance transition metal nitride-based electrocatalysts for hydrogen production. Its electrocatalytic performance can be significantly enhanced by doping transition metal cations.

Phase Evolution on the Hydrogen Adsorption Kinetics of NiFe-Based Heterogeneous Catalysts for Efficient Water Electrolysis.

Transition metal layered double hydroxides, especially nickel-iron layered double hydroxide (NiFe-LDH) shows significant advancement as efficient oxygen evolution reaction (OER) electrocatalyst but also plays a momentous role as a precursor for NiFe-based hydrogen evolution reaction (HER) catalysts. Herein, a simple strategy for developing Ni-Fe-derivative electrocatalysts via phase evolution of NiFe-LDH under controllable annealing temperatures in an argon atmosphere is reported. The optimized catalyst annealed at 340 o C (denoted NiO/FeNi3 ) exhibits superior HER properties with an ultralow overpotential of 16 mV@10 mA cm-2 . Density functional theory simulation and in situ Raman analyses reveal that the excellent HER properties of the NiO/FeNi3 can be attributed to the strong electronic interaction at the interface of the metallic FeNi3 and semiconducting NiO, which optimizes the H2 O and H adsorption energies for efficient HER and OER catalytic processes. This work will provide rational insights into the subsequent development of related HER electrocatalysts and other corresponding compounds via LDH-based precursors.

In Situ Grown Co-Based Interstitial Compounds: Non-3d Metal and Non-Metal Dual Modulation Boosts Alkaline and Acidic Hydrogen Electrocatalysis.

Interfacial engineering and elemental doping are the two parameters to enhance the catalytic behavior of cobalt nitrides for the alkaline hydrogen evolution reaction (HER). However, simultaneously combining these two parameters to improve the HER catalytic properties of cobalt nitrides in alkaline media is rarely reported and also remains challenging in acidic media. Herein, it is demonstrated that high-valence non-3d metal and non-metal integration can simultaneously achieve Co-based nitride/oxide interstitial compound phase boundaries on stainless steel mesh (denoted Mo-Co5.47 N/N-CoO) for efficient HER in alkaline and acidic media. Density functional theory (DFT) calculations show that the unique structure does not only realize multi-active sites, enhanced water dissociation kinetics, and low hydrogen adsorption free energy in alkaline media, but also enhances the positive charge density of hydrogen ions (H+ ) to effectively allow H+ to receive electrons from the catalysts surface toward promoting the HER in acidic media. As a result, the as-prepared Mo-Co5.47 N/N-CoO demands HER overpotential of -28 mV@10 mA cm-2 in an alkaline medium, and superior to the commercial Pt/C at a current density > 44 mA cm-2 in acidic medium. This work paves a useful strategy to design efficient cobalt-based electrocatalysts for HER and beyond.

Sub-Thick Electrodes with Enhanced Transport Kinetics via In Situ Epitaxial Heterogeneous Interfaces for High Areal-Capacity Lithium Ion Batteries.

The ever-growing portable electronics and electric vehicle draws the attention of scaling up of energy storage systems with high areal-capacity. The concept of thick electrode designs has been used to improve the active mass loading toward achieving high overall energy density. However, the poor rate capabilities of electrode material owing to increasing electrode thickness significantly affect the rapid transportation of ionic and electron diffusion kinetics. Herein, a new concept named "sub-thick electrodes" is successfully introduced to mitigate the Li-ion storage performance of electrodes. This is achieved by using commercial nickel foam (NF) to develop a monolithic 3D with rich in situ heterogeneous interfaces anode (Cu3 P-Ni2 P-NiO, denoted NF-CNNOP) to reinforce the adhesive force of the active materials on NF as well as contribute additional capacity to the electrode. The as-prepared NF-CNNOP electrode displays high reversible and rate areal capacities of 6.81 and 1.50 mAh cm-2 at 0.40 and 6.0 mA cm-2 , respectively. The enhanced Li-ion storage capability is attributed to the in situ interfacial engineering within the NiO, Ni2 P, and Cu3 P and the 3D consecutive electron conductive network. In addition, cyclic voltammetry, charge-discharge curves, and symmetric cell electrochemical impedance spectroscopy consistently reveal improved pseudocapacitance with enhanced transports kinetics in this sub-thick electrodes.

Advanced Tri-Layer Carbon Matrices with π-π Stacking Interaction for Binder-Free Lithium-Ion Storage.

Enabling materials with distinct features toward achieving high-performance energy storage devices is of huge importance but highly challenging. Commercial carbon cloth (CC), because of its appealing chemical and mechanical properties, has been proven to be an excellent conductive substrate for active electrode materials. However, its performance is notably poor when directly used as an electrode in energy storage, due to its low theoretical capacity and surface area. Herein, we successfully endow the CC with enhanced storage capacity via formation of a π-π stacking interaction by integrating electrochemically activated CC (denoted CC/ACC) with biomass-derived carbon (BMDC) (denoted π-CC/ECC@BMDC). The π-CC/ECC@BMDC electrode displays excellent storage performance with a high capacity of 2.53 mAh cm-2 under 0.2 mA cm-2 when used as anode material for lithium ion batteries (LIBs). Due to the induction energy, the negatively charged molecules of the CC/ACC functional groups interact with the BMDC during carbonization, creating the π-π stacking interaction. Based on first-principles calculations, the structural design of the tri-layer carbon enables the movement of electrons around the π-π stacking interaction, which significantly facilitates rapid transportation of electrons, creates three-dimensional (3D) ion tunnels for fast transportation of ions, and improves the electrode's mechanical and electronic properties.

Polypyrrole Hollow Microspheres with Boosted Hydrophilic Properties for Enhanced Hydrogen Evolution Water Dissociation Kinetics.

The water dissociation step (H2O + M + e- → M - Hads + OH-) is a crucial one toward achieving high-performance hydrogen evolution reaction (HER). The application of electronic conducting polymers (ECPs), such as polypyrrole (PPy), as the electrocatalyst for HER is rarely reported because of their poor adsorption energy per water molecule, which hinders the Volmer step. Herein, we strongly enrich PPy hollow microspheres (PPy-HMS) with attractive HER activity by enhancing their hydrophilic properties through hybridization with good water affinity SiO2. The as-prepared PPy-coated SiO2 (PPy@SiO2-HMS) achieves a current density of 10 mA cm-2 at -123 mV, which is lower than that of pristine PPy-HMS (-192 mV). Raman and X-ray photospectroscopy analyses reveal that the enhanced HER catalytic capability can be attributed to the strong electronic couplings between PPy and SiO2, and this improves the adsorption energy per water molecule and in turn accelerates the water dissociation kinetics on PPy. This work highlights the potential application of low-cost ECPs as promising electrocatalysts for water electrolysis.

Asymmetric Pseudocapacitors Based on Interfacial Engineering of Vanadium Nitride Hybrids.

Vanadium nitride (VN) shows promising electrochemical properties as an energy storage devices electrode, specifically in supercapacitors. However, the pseudocapacitive charge storage in aqueous electrolytes shows mediocre performance. Herein, we judiciously demonstrate an impressive pseudocapacitor performance by hybridizing VN nanowires with pseudocapacitive 2D-layered MoS2 nanosheets. Arising from the interfacial engineering and pseudocapacitive synergistic effect between the VN and MoS2, the areal capacitance of VN/MoS2 hybrid reaches 3187.30 mF cm-2, which is sevenfold higher than the pristine VN (447.28 mF cm-2) at a current density of 2.0 mA cm-2. In addition, an asymmetric pseudocapacitor assembled based on VN/MoS2 anode and TiN coated with MnO2 (TiN/MnO2) cathode achieves a remarkable volumetric capacitance of 4.52 F cm-3 and energy density of 2.24 mWh cm-3 at a current density of 6.0 mA cm-2. This work opens a new opportunity for the development of high-performance electrodes in unfavorable electrolytes towards designing high areal-capacitance electrode materials for supercapacitors and beyond.

A Simple and Scalable Approach To Remarkably Boost the Overall Water Splitting Activity of Stainless Steel Electrocatalysts.

The stainless steel mesh (SSM) has received growing consideration as an electrocatalyst for efficient hydrogen and oxygen evolution reactions. Recently, the application of SSM as an oxygen evolution reaction (OER) electrocatalyst has been more promising, while its hydrogen evolution reaction (HER) catalytic activity is very low, which definitely affects its overall water splitting activity. Herein, a simple chemical bath deposition (CBD) method followed by phosphorization is employed to significantly boost the overall water splitting performance of SSM. The CBD method could allow the voids between the SSM fibers to be filled with Ni and P. Electrocatalytic studies show that the CBD-treated and phosphorized stainless steel (denoted SSM-Ni-P) exhibits an HER overpotential of 149 mV, while the phosphorization-free CBD-treated SSM (denoted as SSM-Ni) delivers an OER overpotential of 223 mV, both at a current density of 10 mA cm-2. An asymmetric alkaline electrolyzer assembled based on the SSM-Ni-P cathode (HER) and SSM-Ni anode (OER) achieved an onset and 10 mA cm-2 current densities at an overall potential of 1.62 V, granting more prospects for the application of inexpensive and highly active electrocatalysts for electrocatalytic water splitting reactions.

Co3 O4 @Cu-Based Conductive Metal-Organic Framework Core-Shell Nanowire Electrocatalysts Enable Efficient Low-Overall-Potential Water Splitting.

In the work reported herein, the electrocatalytic properties of Co3 O4 in hydrogen and oxygen evolution reactions have been significantly enhanced by coating a shell layer of a copper-based metal-organic framework on Co3 O4 porous nanowire arrays and using the products as high-performance bifunctional electrocatalysts for overall water splitting. The coating of the copper-based metal-organic framework resulted in the hybridization of the copper-embedded protective carbon shell layer with Co3 O4 to create a strong Cu-O-Co bonding interaction for efficient hydrogen adsorption. The hybridization also led to electronically induced oxygen defects and nitrogen doping to effectively enhance the electrical conductivity of Co3 O4 . The optimal as-prepared core-shell hybrid material displayed excellent overall-water-splitting catalytic activity that required overall voltages of 1.45 and 1.57 V to reach onset and a current density of 10 mA cm-2 , respectively. This is the first report to highlight the relevance of hybridizing MOF-based co-catalysts to boost the electrocatalytic performance of nonprecious transition-metal oxides.

Efficient Hydrogen Evolution Activity and Overall Water Splitting of Metallic Co4N Nanowires through Tunable d-Orbitals with Ultrafast Incorporation of FeOOH.

Cobalt nitride electrocatalysts have been investigated and proven to show excellent oxygen evolution reaction activity owing to their excellent metallic properties, but their hydrogen evolution reaction (HER) properties are rarely reported because of their unsatisfactory molecular energy level, especially the d-orbital. Herein, taking Co4N as a case study, we tune the d-orbital of metallic Co4N nanowires via rapid formation of iron oxyhydroxide (FeOOH). Experimental analyses show that FeOOH@Co4N/SSM exhibits excellent HER catalytic activity with considerable low onset overpotential (22 mV), small Tafel slope (34 mV dec-1), and excellent stability at current densities ranging from 20 to 100 mA cm-2. Additionally, theoretical assessments display that the hybridization of Co4N with FeOOH is beneficiary for optimizing and promoting the free energy of H adsorption due to the tuning of d-orbital. An overall water-splitting device assembled based on bifunctional FeOOH@Co4N/SSM delivers an onset potential of 1.48 V with excellent stability up to 4 days. This shows a new strategy for designing a high-performance water-splitting device based on cobalt-based electrocatalysts.