In Situ Antisolvent Approach to Hydrangea-like HCo3 O4 -NC@CoNi-LDH Core@Shell Superstructures for Highly Efficient Water Electrolysis

NiFe-Coordination Polymers-Derived Layered Double Hydroxides as Bifunctional Materials: Effect of the Ni : Fe Ratio on the Electrochemical Performance

The development of an efficient and cost-effective material is highly desirable for electrochemical devices such as electrolyzers and supercapacitors. Especially, pseudomorphic transformations of metal-organic frameworks (MOFs)/coordination polymers (CPs) into layered double hydroxides (LDHs) materials endow well-defined porosities, high surface area, exchangeable interlayer anions and easily adjustable electronic structure that are truly required for oxygen evolution reaction (OER) and high-performance supercapacitor applications. Herein, we have prepared NiFe-LDHs of various Ni/Fe ratios via a facile room-temperature alkaline hydrolysis of NiFe-CPs precursors. Electrochemical studies reveal that the catalyst having high amount of Fe (Ni1.2 Fe1 -LDH) showed the better OER activity with a low Tafel slope (65 mV dec-1 ) in 1 M KOH. On the other hand, the catalyst containing higher amount of Ni with better layered structure (Ni11.7 Fe1 -LDH) showed high performance for supercapacitor (702 F g-1 at 0.25 A g-1 ) in 3 M KOH. Moreover, a solid-state asymmetric supercapacitor device Ni11.7 Fe1 -LDH/AC was fabricated which exhibited a specific capacitance of 18 F g-1 at a current density of 1 A g-1 . The device displayed high cycling stability with 88% of capacitance retention after 7000 cycles. The experimental findings in this work will help in the futuristic development of NiFe-LDH based electrocatalysts for the enhanced electrochemical performances.

Electrodeposition of Defect-Rich Ternary NiCoFe Layered Double Hydroxides: Fine Modulation of Co3+ for Highly Efficient Oxygen Evolution Reaction

The low-cost, high-abundance and durable layered double hydroxides (LDHs) have been considered as promising electrocatalysts for oxygen evolution reaction (OER). However, the easy agglomeration of lamellar LDHs in the aqueous phase limits their practical applications. Herein, a series of ternary NiCoFe LDHs were successfully fabricated on nickel foam (NF) via a simple electrodeposition method. The as-prepared Ni(Co_0.5 Fe_0.5 )/NF displayed an unique nanoarray structural feature. It showed an OER overpotential of 209 mV at a current density of 10 mA cm^-2 in alkaline solution, which was superior to most systems reported so far. As evidenced by the XPS and XAFS results, such excellent performance of Ni(Co_0.5 Fe_0.5 )/NF was attributed to the higher Co³⁺ /Co²⁺ ratio and more defects exposed, comparing with Ni(Co_0.5 Fe_0.5 )-bulk and Ni(Co_0.5 Fe_0.5 )-mono LDHs prepared by conventional coprecipitation method. Furthermore, the ratio of Co to Fe could significantly tune the Co electronic structure of Ni(Co_x Fe_1-x )/NF composites (x=0.25, 0.50 and 0.75) and affect the electrocatalytic activity for OER, in which Ni(Co_0.5 Fe_0.5 )/NF showed the lowest energy barrier for OER rate-determining step (from O* to OOH*). This work proposes a facile method to develop high-efficiency OER electrocatalysts.

Co9S8 nanowires@NiCo LDH nanosheets arrays on nickel foams towards efficient overall water splitting

Water electrolysis is considered to be an effective way to fabricate hydrogen, and it is desirable to find the highly efficient, inexpensive and good durability bifunctional electrocatalysts for overall water splitting. In this paper, we synthesis a unique structured catalyst that was composed by Co₉S₈ nanowires and nickel cobalt layered double hydroxide (NiCo-LDH) nanosheets. The ultrathin nanosheets decorated on the Co₉S₈ nanoarrays offer large specific surface area, numerous active edge sites and excellent electrical conductivity for fast electron transfer. Benefiting from this heterogeneous structure, the catalyst presents excellent catalytic performance in alkaline media. It requires 168 mV to reach current density of 10 mA/cm² for HER and 278 mV to reach current density of 30 mA/cm² for OER. When used as electrode in a homemade two-electrode system, it only needs t a voltage of 1.63 V to achieve current densities of 10 mA/cm², which proves Co₉S₈@NiCo LDH/NF as a superior bifunctional catalyst for water splitting.

Clean synthesis of ZnCo2O4@ZnCo-LDHs yolk–shell nanospheres composed of ultra-thin nanosheets with enhanced electrocatalytic properties

ZnCo₂O₄@ZnCo-LDHs yolk–shell nanospheres are prepared by a clean approach via controlled hydrolysis of mixed metal glycolates. The structures exhibit good oxygen evolution reaction activity.

Engineering Cu2O/Cu@CoO hierarchical nanospheres: synergetic effect of fast charge transfer cores and active shells for enhanced oxygen evolution reaction

An OER catalyst that has a high conductivity Cu₂O/Cu core and a strong bonding interface with the active CoO shell was constructed.

Construction of a hierarchical NiFe layered double hydroxide with a 3D mesoporous structure as an advanced electrocatalyst for water oxidation

A facile and cost-effective one-step hydrothermal method is used to synthesize NiFe LDH microclusters with a 3D hierarchically mesoporous architecture. This superior electrocatalyst can achieve a current density of 10 mA cm⁻² with an ultralow overpotential of 211 mV toward the oxygen evolution reaction.