Transition metal-based layered double hydroxides (LDHs) have been capable of working efficiently as catalysts in the basic oxygen evolution reaction (OER) for sustaining hydrogen production of alkaline water electrolysis. Nevertheless, exploring new LDH-based electrocatalysts featuring both remarkable activity and good stability is still in high demand, which is pivotal for comprehensive understanding and impressive improvement of the sluggish OER kinetics. Here, a series of bimetallic (Co and Mo) LDH arrays were designed and fabricated via a facile and controlled strategy by incorporating a Mo source into presynthesized Co-based metal-organic framework (MOF) arrays on carbon cloth (CC), named as ZIF-67/CC arrays. We found that tuning the Mo content resulted in gradual differences in the structural properties, surface morphology, and chemical states of the resulting catalysts, namely CoMo_x-LDH/CC (x representing the added weight of the Mo source). Gratifyingly, the best-performing CoMo_0.20-LDH/CC electrocatalyst demonstrates a low overpotential of only 226 mV and high stability at a current density of 10 mA·cm⁻², which is superior to most LDH-based OER catalysts reported previously. Furthermore, it only required 1.611 V voltage to drive the overall water splitting device at the current density of 10 mA·cm⁻². The present study represents a significant advancement in the development and applications of new OER catalysts.

Zn-air batteries (ZABs) as a class of promising energy storage setups are generally powered by efficient and robust catalysts at the oxygen-involving cathode. Although the existing non-noble catalysts have outperformed noble Pt benchmark in the alkaline liquid-state ZABs, to the best of our knowledge few have excelled Pt in quasi-solid-state (QSS) ZABs. Herein, we found that an integrated Mn-Co cathode derived from the bimetallic Mn/Co metal organic frameworks generates a 1.4-fold greater power density in the QSS ZABs than a Pt cathode while its power density in liquid-state ZABs is only 0.8-fold of the latter. Moreover, such Mn-Co catalyst delivers high-rate oxygen reduction reaction (ORR) capability with half-wave potential of 0.84 V. The in-depth characterizations and analyses have demonstrated that the Co and Mn species show the specific affinity towards H₂O and O₂, respectively, synergizing the ORR process in the water-deficient environment of QSS ZABs. This work has enlightened the rational design of non-noble metal catalysts to improve the power density of QSS ZABs.

Graphene oxide (GO)-based membranes have been widely studied for realizing efficient wastewater treatment, due to their easily functionalizeable surfaces and tunable interlayer structures. However, the irregular structure of water channels within GO-based membrane has largely confined water permeance and prevented the simultaneously improvement of purification performance. Herein, we purposely construct the well-structured three-dimensional (3D) water channels featuring regular and negatively-charged properties in the GO/SiO₂ composite membrane via in situ close-packing assembly of SiO₂ nanoparticles onto GO nanosheets. Such regular 3D channels can improve the water permeance to a record-high value of 33,431.5 ± 559.9 L·m⁻²·h⁻¹ (LMH) bar⁻¹, which is several-fold higher than those of current state-of-the-art GO-based membranes. We further demonstrate that benefiting from negative charges on both GO and SiO₂, these negatively-charged 3D channels enable the charge selectivity well toward dye in wastewater where the rejection for positive-charged and negative-charged dye molecules is 99.6% vs. 7.2%, respectively. The 3D channels can also accelerate oil/water (O/W) separation process, in which the O/W permeance and oil rejection can reach 19,589.2 ± 1,189.7 LMH bar⁻¹ and 98.2%, respectively. The present work unveils the positive role of well-structured 3D channels on synchronizing the remarkable improvement of both water permeance and purification performance for highly efficient wastewater treatment.

Rational design of oxygen evolution reaction (OER) catalysts at low cost would greatly benefit the economy. Taking advantage of earth-abundant elements Si, Co and Ni, we produce a unique-structure where cobalt-nickel silicate hydroxide [Co_2.5Ni_0.5Si₂O₅(OH)₄] is vertically grown on a reduced graphene oxide (rGO) support (CNS@rGO). This is developed as a low-cost and prospective OER catalyst. Compared to cobalt or nickel silicate hydroxide@rGO (CS@rGO and NS@rGO, respectively) nanoarrays, the bimetal CNS@rGO nanoarray exhibits impressive OER performance with an overpotential of 307 ​mV@10 ​mA ​cm⁻². This value is higher than that of CS@rGO and NS@rGO. The CNS@rGO nanoarray has an overpotential of 446 ​mV@100 ​mA ​cm⁻², about 1.4 times that of the commercial RuO₂ electrocatalyst. The achieved OER activity is superior to the state-of-the-art metal oxides/hydroxides and their derivatives. The vertically grown nanostructure and optimized metal-support electronic interactions play an indispensable role for OER performance improvement, including a fast electron transfer pathway, short proton/electron diffusion distance, more active metal centers, as well as optimized dual-atomic electron density. Taking advantage of interlay chemical regulation and the in-situ growth method, the advanced-structural CNS@rGO nanoarrays provide a new horizon to the rational and flexible design of efficient and promising OER electrocatalysts.

Zeolitic-imidazole frameworks (ZIFs) derivations have widely emerged as an efficient air cathode of zinc-air batteries (ZABs) due to excellent bifunctional oxygen electrocatalysis performance. However, they are not stable enough for long-term operation of rechargeable ZABs because of weak association with current collector, especially under bending conditions for flexible ZAB devices. Here, we show that by purposely designing coordinatively unsaturated ZIFs via a facile morphology regulation, which can be chemically linked on acid-treated carbon cloth, a stable Co-N-C air cathode is therefore derived where Co nanoparticles (NPs) are uniformly confined within the Co-N-C matrix on carbon cloth (Co/Co-N-C/CC). Specifically, when without being stabilized from carbon cloth, the pyrolysis of ZIFs with different unsaturated coordination levels has a negligible impact on the bifunctional oxygen-catalyzed performance. The optimal Co/Co-N-C/CC catalyst assembled ZAB possesses a large open circuit voltage of 1.415 V and a high peak power density of 163 mW·cm⁻² as well as excellent cycling durability upon 630 discharge–charge cycles with 61% voltage efficiency remained, largely exceeding those of a benchmark Pt/C-IrO₂ catalyst assembled ZAB. The synergy between Co NPs and active Co-N-C sites via electronic interaction induces the outstanding bifunctional oxygen-catalyzed activity and cathode performance. The present work highlights the importance of unsaturated coordination structures in ZIFs precursors for the performance of derived nanostructures in integrated electrodes.

Designing hierarchical heterostructure to optimize the adsorption of hydrogen intermediate (H*) is impressive for hydrogen evolution reaction (HER) catalysis. Herein, we show that vertically mounting two-dimensional (2D) layered molybdenum disulfide (MoS₂) nanosheets on 2D nonlayered dimolybdenum carbide (Mo₂C) nanomeshes to form a hierarchical heterostructure largely accelerates the HER kinetics in acidic electrolyte due to the weakening adsorption strength of H* on 2D Mo₂C nanomeshes. Our hierarchical MoS₂/Mo₂C heterostructure therefore gives a decrease of overpotential for up to 500 mV at −10 mA·cm⁻² and an almost 200-fold higher kinetics current density compared with the pristine Mo₂C nanomeshes and maintains robust stability with a small drop of overpotential for only 16 mV upon 5,000 cycles. We further rationalize this finding by theoretical calculations and find an optimized adsorption free energy of H*, identifying that the MoS₂ featuring strong H* desorption plays a key role in weakening the strong binding of Mo₂C with H* and therefore improves the intrinsic HER activity on active C sites of Mo₂C. This present finding shines the light on the rational design of heterostructured catalysts with synergistic geometry.