The Al effect on the electrochemical properties of layered double hydroxides (LDHs) is not properly probed, although it is demonstrated to notably promote the capacitive behavior of LDHs. Herein, ternary NiCo 2 Al x layered double hydroxides with varying levels of Al stoichiometry are purposely developed, grown directly on mechanically flexible and electrically conducting carbon cloth (CC@NiCo 2 Al x -LDH). Al plays a significant role in determining the structure, morphology, and electrochemical behavior of NiCo 2 Al x -LDHs. At an increasing level of Al in NiCo 2 Al x -LDHs, there is a steady evolution from 1D nanowire to 2D nanosheets. The CC@NiCo 2 Al-LDH at an appropriate level of Al and with the nanowire-nanosheet mixed morphology exhibits both significantly enhanced electrochemical performance and excellent structural stability, with about a 2.3-fold capacitance of NiCo 2 -OH. When applied as the anode in a flexible asymmetric supercapacitor (ASC), the CC@NiCo 2 Al-LDH gives rise to a remarkable energy density of 44 Wh kg −1 at the power density of 462 W kg −1 , together with remarkable cyclic stability with 91.2% capacitance retention over 15 000 charge-discharge cycles. The present study demonstrates a new pathway to significantly improve the electrochemical performance and stability of transition metal LDHs, which are otherwise unstable in structure and poorly performing in both rate and cycling capability.

Developing highly active oxygen evolution reaction (OER) catalysts with fast OER kinetics is crucial for disruptively changing the energy technology, where unlocking of the catalytic origin is the key to the rational design of high-performance catalysts. Herein, a Co-based heterostructure consisting of cobalt (Co) and molybdenum carbide (Mo 2 C) nanoparticles in a 2D morphology is purposely designed as an OER precatalyst. At the initial stage of the OER in alkaline solution, the fast phase transition of Co metal into γphase cobalt oxyhydroxide (γ-CoOOH) in the presence of Mo 2 C gives rise to a Mo-enriched surface of the defective γ-CoOOH. This significantly raises the OER kinetics and gives an almost 90% enhancement in catalytic activity per metal site. Interestingly, the phase transition to γ-CoOOH and Mo-enriched surface reconstruction are potential-dependent and are accelerated at 1.4 V, as revealed by in situ Raman spectroscopy as well as ex situ scanning transmission electron microscopy studies. Potential-dependent X-ray photoelectron spectroscopy analyses and methanol oxidation experiments further confirm that the Mo enrichment into the defective CoOOH surface promotes electron flow from Mo to Co sites via the bridging oxygen, greatly benefiting the electrostatic adsorption of OH − ions and smoothing the subsequent OER steps.

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