Formation of Ni-Fe Mixed Diselenide Nanocages as a Superior Oxygen Evolution Electrocatalyst.

An effective low-cost nano NiO-In2O3 electrode material for oxygen evolution (OER) is presented. Electrochemical studies uncovered electrocatalytic recital in Ascorbic Acid, Hydrogen Peroxide (H2O2), and ethanol. The cubic crystal structure of NiO-In2O3 was revealed by XRD. FT-IR, FE-SEM and HR-TEM studies exploit the structure and morphology of NiO-In2O3. Electrochemistry of NiO-In2O3 uncovered high current density (900mA/cm2) at substantially low overpotential (230mV), realizing its OER recital. On top, high mass activity and turnover frequency by NiO-In2O3 comprehend improved electrical and semiconductive properties in H2O2. The NiO-In2O3 durability beyond 90 hours was estimated by chronopotentiometry (CP). The Impedance analysis (EIS) revealed low charge transfer resistance and high exchange current density. Given electrocatalytic studies, we found a direct relationship between NiO-In2O3 nanocomposite and the degradation of H2O2 compared to its counterparts. Hence, this strategy can be an alternative and potential source of hydrogen and oxygen production at commercial scale. Highlights A facile and effectual low-cost NiO-In2O3 electrocatalyst is developed for efficient OER in aqueous hydrogen peroxide. NiO-In2O3 nanocomposite showed high current density (900mA/cm2) at low overpotential grasping its oxygen evolution reaction (OER) concert. NiO-In2O3 Impedance analysis revealed its low charge transfer resistance, high exchange current density (J exc.), high mass Activity, and high turnover frequency (TOF) in hydrogen peroxide, advocating enhanced electrical and semiconductive properties. NiO-In2O3 showed long-term durability (>90 h) at varying current densities, fostering its application as a potential electrocatalyst for OER/HER reactions.

Hydrogen (H2) is one of the most promising energy carriers for future clean energy production. The cleanest method to produce H2 is by water electrolysis using renewable electricity. Among electrolysis technologies, alkaline water electrolysis (AWE) is significantly cheaper than other techniques. While AWE is cost effective, it suffers from low power densities due to limited electrochemical stability at high current densities. Most stability challenges arise from anode degradation, where the oxygen evolution reaction (OER) occurs. The OER is key to achieve economic viability of AWE and current state-of-the-art electrocatalysts for OER are costly and scarce. Nickel-based catalysts are inexpensive, earth-abundant, and exhibit high OER performance but still exhibit durability challenges under high current densities. While several approaches have been reported to enhance durability of these catalysts, they are often complicated and time-consuming. We present a novel and simple method through which external stimulation can be used to enhance the durability of single metal catalysts. In this work, the durability of nickel-based electrocatalysts for OER under alkaline conditions (1 M NaOH) at high current densities was evaluated as a function of external stimulation in a chemically stable custom electrochemical cell. This cell was fabricated using additive manufacturing (AM), which enabled the direct application of external stimulation onto nickel-based materials in the cell. In addition, the performance of the electrocatalysts at high OER current densities for extended periods of time was measured as a function of various external stimulation parameters. Acknowledgements Financial support from the Los Alamos National Laboratory, Laboratory-Directed Research and Development (LDRD) is gratefully acknowledged. The authors would also like to thank the NNSA Minority Serving Institutes Partnership Program and LANL: Under-Represented Minority Partnership Program for their funding support. References Vij, Varun, et al. "Nickel-based electrocatalysts for energy-related applications: oxygen reduction, oxygen evolution, and hydrogen evolution reactions." Acs Catalysis10 (2017): 7196-7225.Foroughi, Faranak, et al. "Understanding the Effects of Ultrasound (408 kHz) on the Hydrogen Evolution Reaction (HER) and the Oxygen Evolution Reaction (OER) on Raney-Ni in Alkaline Media." Ultrasonics Sonochemistry 84 (2022): 105979.Foroughi, Faranak, et al. "Sonoactivated polycrystalline Ni electrodes for alkaline oxygen evolution reaction." Ultrasonics Sonochemistry 86 (2022): 106013.

A facile and effective strategy for fabricating a three-dimensionally (3D) structured nanocomposite catalyst based on nonprecious metals for water splitting in alkaline electrolyzers is reported in this paper. This nanocomposite catalyst consists of the CdS quantum dots (QDs) decorated Ni3S2 nanosheet flowers deposited on the plasma-treated nickel foam (PNF). The NiO formed during the plasma treatment is shown to play an important role for pushing the hydrogen and oxygen evolution reactions (HER and OER) in alkaline media. The enhanced exposure of active sites on the nanopetalages results in superior catalytic performance for promoting HER and OER in alkaline electrolyzers. Specifically, a current density of 10 mA cm-2 can be achieved for the HER with a 121 mV overpotential when the working electrode based on the 1 mM CdS/Ni3S2/PNF catalyst is employed in 1 M KOH. The corresponding Tafel slope is 110 mV/decade. For the OER, the onset potential can be as low as 1.25 V vs reversible hydrogen electrode (RHE) reference electrode, which is substantially lower than the commercial IrO2 catalyst (∼1.47 V). This nanostructured catalyst has excellent long-term stability, and the linear scan voltammetry (LSV) curves of the HER and OER in 1 M KOH solution show negligible decay after undergoing 104 cycles of cyclic voltammogram. The nanocomposite material developed in this study is an ideal candidate as a catalyst for splitting water in alkaline media with relatively low overpotentials at reasonably high current densities (≥100 mA cm-2).

Efficient ways to perform electrolysis of water to form hydrogen and oxygen gas has far reaching consequences regarding in the energy sector. Hydrogen is considered to be fuel alternative to fossil fuels and electrolysis is regarded as a large-scale storage option for renewable energy as chemical fuels from sources such as wind and solar. In the electrolysis of water, the oxygen evolution reaction (OER) is the rate-limiting step and thus provides multiple opportunities to improve overall performance. Development of electrocatalysts with low overpotential, low Tafel slope, high mass activity, and high turn-over frequency (TOF) in alkaline medium that will expedite the reaction is crucial. Non precious metals such as iron, nickel, and cobalt may be the solution to the slow kinetics of the OER. In recent literature, bimetallic nanowires with these three metals have shown promising results. Nanowires can be synthesized using a simple hydrothermal process which is amenable to large scale production. Yang et al. have synthesized NiCoO2 nanowires with a small overpotential (~0.303 V) at a current density of 10mA cm-2 and low Tafel slope (~57 mV dec- 1).1 Fang et al. have synthesized NiCoS2 nanowires with small overpotential (~0.27V) to afford a current density of 10mA cm-2 and a low Tafel slope (~119mV dec-1).2 Recent work on bimetallic layered double hydroxide (LDH) nanoparticles have also yielded positive results. Zhu et al. fabricated a novel NiFe-LDH/nanocarbon hybrid with small overpotential (~0.35V) at a current density of 10mA cm-2 and a low Tafel slope (~54mV dec-1).3 Li et al. developed NiFe-LDH array with a small overpotential of (~0.224V) at a current density of 10mA cm-2.4 This research will build on these recent published work with a focus on synthesizing nanoparticles and nanowires with an optimal ratio of metals, as the ratio of metals in a multimetallic nanostructure is likely to factor heavily in the electrochemical activity. Our research will also attempt to identify preferred nanocatalyst candidates for electrocatalyst performance in alkaline solution. In this presentation, we will report on our work thus far in comparing the electrochemical performance and material characterization of nanocatalysts synthesized with different metal compositions, as well as comparing nanoparticle morphology to nanowire morphology. Imaging techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) will be used to study the morphology of the particles. Elemental analysis and characterization of nanocatalyst phase and surface chemistry will be performed using energy dispersive x-ray spectroscopy (EDX), x-ray photoelectron spectroscopy (XPS), and powder x-ray diffraction (XRD). Electrochemical analysis using cyclic voltammetry will also be performed on the bimetallic nanomaterials. Experiments on the stability of the materials will also be conducted using chronoamperometry.

Developing stable, efficient, and affordable Earth-abundant transition metal-based electrocatalysts for water splitting applications is key to producing green hydrogen. This study reports the development of new Ni(II)-based one-dimensional coordination polymers (CPs), namely, [Ni(9-AnBz)2(4,4'-bpy)2(MeOH)2] (CP 1), [Ni(9-AnBz)2(4,4'-bpe)2(MeOH)2] (CP 2), and [Ni(9-AnBz)2(3,3'-bpdb)2(H2O)2]·H2O (CP 3) (where 9-AnBz = 9-anthracenyl-4'-benzoate, 4,4'-bpy = 4,4'-bipyridine, 4,4'-bpe = trans-1,2-bis(4'-pyridyl)ethene, and 3,3'-bpdb = 1,4-bis(3'-pyridyl)-2,3-diaza-1,3-butadiene), as novel electrocatalysts. Their structures have been confirmed by single crystal X-ray diffraction. These Ni(II)-based CPs exhibited improved electrocatalytic activity towards both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in 1.0 M KOH. The CP 1 catalyst was found to deliver a low HER onset potential (∼-0.04 V vs. RHE), a small HER overpotential (∼87 mV at -10 mA cm-2), a Tafel slope of ∼107.0 mV dec-1, high current density (-496 mA cm-2 at ∼1.83 V vs. RHE), and high mass activity (∼50.0 A g-1), comparable to those of commercial Pt/C. Moreover, the CP 1 catalyst also exhibited the best OER activity, with a small overpotential (∼370 mV at 10 mA cm-2) and a low Tafel slope (∼82 mV dec-1), showing efficient performance and great promise in hydrogen production systems.

The hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) were studied at electrodeposited Ni-Sn alloys. All coatings were electrodeposited onto a Ni 40 mesh substrate from a bath containing Ni and Sn ions in the presence of pyrophosphate and glycine. The electrodes were investigated by cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electrochemical impedance spectroscopy (EIS) and polarization measurements. It was shown that among the increase of the roughness factor of Ni- Sn coatings with the increase of electrodeposition current density, their composition was also responsible for their catalytic activity for both, the HER and the OER. In the potential range of the HER two regions were observed, but none of them was characterized with the linear dependence E vs. log j (Tafel slope). For the OER two Tafel slopes were detected: one of about 60 mV dec-1 at lower current densities (up to about 20 mA cm-2) and one of about 120 mV dec-1 at higher current densities. Based on the Tafel slopes and EIS results the mechanisms for the HER and OER were proposed and discussed.

Hydrogen energy has become one of the most promising substitutes for conventional fuels because of its high calorific value and green and renewable advantages. Among various hydrogen production strategies, the water splitting hydrogen production strategy stands out. Therefore, it is very important to develop efficient and cheap oxygen evolution reaction (OER) electrocatalysts for hydrogen production by electrolysis of water. In this work, nickel selenide grown on nickel foam (NF) with good electrical conductivity and excellent catalytic performance, i.e. NiSex/NF, was selected as the three-dimensional conducting substrate, and the active material ZIF-67 was successfully compounded on the conductive substrate by using the in situ growth strategy. A series of self-supporting materials ZIF-67/NiSex/NF were obtained, which can be directly used as working electrodes for the electrocatalytic OER. The self-supporting material ZIF-67/NiSex/NF-1 can achieve a low overpotential of 353 mV at a current density of 100 mA cm-2 with a small Tafel slope of 107 mV dec-1, and excellent stability for 55 hours of continuous OER at a current density of 50 mA cm-2 in an alkaline medium. Benefiting from the unique layered structure and the synergy between Co and Se optimizing the electronic structure, ZIF-67/NiSex/NF-1 when used directly as an electrode shows exceptional OER catalytic performance at high current density.

Designing a highly efficient transition-metal-based electrocatalyst for the oxygen evolution reaction (OER) in an alkaline electrolyte by a green and low-cost protocol is still facing many challenges. Herein, a regular-hexahedron-shaped iron-copper oxide (CuFe2O4-Fe2O3) is engineered on plasma-treated iron foam (PFF) with a one-step hydrothermal process. Benefiting from the formed rich heterointerfaces, the obtained CuFe2O4-Fe2O3/PFF exhibits an outstanding OER activity and stability in the alkaline medium, and the overpotential for delivering a current density of 10 mA cm-2 (j10) is only 190 mV. Meanwhile, thanks to the micronized hexahedron profile, CuFe2O4-Fe2O3/PFF also shows an excellent electrocatalytic stability, and the OER activity decays only 8% after a 90 h OER test under a high current density (j100). Furthermore, the theory calculation (DFT) indicates that Fe sites exposed on the heterointerface of CuFe2O4 and Fe2O3 are the main active centers for O2 evolution in an alkaline medium.

Improving the kinetics of the oxygen evolution reaction (OER) is critical for the widespread adoption and application of water electrolysis technology, which has become a key strategy in addressing energy and environmental challenges. Ni-based transition metal alloy catalysts offer several advantages, including high catalytic capability, tunable composition, low cost, excellent corrosion resistance, and environmental friendliness, making them highly attractive for catalyzing OER in alkaline electrolysis. In this study, we synthesized a series of highly ordered mesoporous NiCoFe alloy nanospheres (OM-NiCoFe) with varying elemental compositions and uniform sphere diameters using a facile wet chemical reduction method and evaluated their OER performance in alkaline media. Owing to their unique ordered mesoporous structure, which promotes mass transport, increases specific surface area, and enhances the accessibility of active sites, combined with the synergistic catalytic effect among different metal elements, the OM-NiCoFe catalysts achieved high current densities (>500 mA cm-2) at potentials below 1.7 V vs RHE during the OER process. Notably, the OM-Ni47Co35Fe18 sample, with the optimal elemental composition, exhibited a low overpotential of 193 mV at 10 mA cm-2, a small Tafel slope of 32.2 mV dec-1, and excellent stability (with negligible potential change at a current density of 200 mA cm-2 for 120 h), outperforming other reference samples and most Ni-based OER electrocatalysts. This work presents an effective strategy for preparing ordered mesoporous spherical metallic materials that not only deliver competitive OER performance but also offer a versatile platform for applications in energy conversion and storage, adsorption, and magnetism.

Designing a state-of-the-art nonprecious oxygen evolution reaction (OER) electrocatalyst with ultralong stability under high current density (≥100 h under 1000 mA cm-2) is greatly desirable for the viable electrolysis of water. The synthesis of nanostructure catalysts is an effective method for improving the OER performance, but nanostructure-based catalysts are easily destroyed by mechanical force via the vigorous oxygen gas evolution process at a high current density. Herein, we present a facile strategy of N-anion and Fe-cation dual doping to construct a three-dimensional self-supported nickel selenide film-based catalyst via a one-step chemical vapor deposition process. The film exhibits outstanding OER activity with a small Tafel slope of 34.86 mV dec-1 and an overpotential of 267 mV at 100 mA cm-2 in 1 M KOH media. Impressively, the film-based catalyst can maintain this excellent catalytic activity over 100 h, even when operated at a high current density of 1 A cm-2, thus exhibiting the best reported OER stability under high current density so far. Further studies reveal that anion-cation co-doping can simultaneously modulate the electronic state and phase structure of nickel selenide, thereby promoting the in situ formation and transformation of oxygen-vacancy-rich amorphous OER active species and resulting in the superior OER performance of the film-based catalyst.

Developing low-cost and highly-efficient non-precious metal bifunctional electrocatalysts towards the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is an attractively alternative strategy to solve the environmental pollution problems and energy demands. In this study, metal-organic framework (MOF) derived porous cobalt poly-phosphide (CoP3) concave polyhedrons are prepared and explored as superior bifunctional electrocatalysts for the HER and OER. The prepared MOF derived CoP3 concave polyhedrons show excellent electrocatalytic activity and stability towards the HER and OER in both acidic and alkaline media, with the Tafel slopes of 53 mV dec-1 and 76 mV dec-1 and a current density of 10 mA cm-2 at the overpotentials of -78 and 343 mV for the HER and OER, respectively, which are remarkably superior to those of the transition metal phosphides (TMPs) and comparable to those of the commercial precious metal catalysts. In addition, they also offer efficient catalytic activities and durabilities under neutral and basic conditions for the HER. The results of our study may shed light on the direction towards highly efficient bifunctional TMP electrocatalysts with high phosphorous component.

Electrochemical water splitting into hydrogen and oxygen is a promising technology for sustainable energy storage. The development of earth-abundant transition metal phosphides (TMPs) to catalyze the hydrogen evolution reaction (HER) and TMP-derived oxy-hydroxides to catalyze the oxygen evolution reaction (OER) has recently drawn considerable attention. However, most monolithically integrated metal phosphide electrodes are prepared by laborious multi-step methods and their operational stability at high current densities has been rarely studied. Herein, we report a novel vapor-solid synthesis of single-crystalline cobalt phosphide nanowires (CoP NWs) on a porous Co foam and demonstrate their use in overall water splitting. The CoP NWs grown on the entire surface of the porous Co foam ligaments have a large aspect ratio, and hence are able to provide a large catalytically accessible surface over a given geometrical area. Comprehensive investigation shows that under the OER conditions CoP NWs are progressively and conformally converted to CoOOH through electrochemical in situ oxidation/dephosphorization; the latter serving as an active species to catalyze the OER. The in situ oxidized electrode shows exceptional electrocatalytic performance for the OER in 1.0 M KOH, delivering 100 mA cm-2 at an overpotential (η) of merely 300 mV and a small Tafel slope of 78 mV dec-1 as well as excellent stability at various current densities. Meanwhile, the CoP NW electrode exhibits superior catalytic activity for the HER in the same electrolyte, affording -100 mA cm-2 at η = 244 mV and showing outstanding stability. An alkaline electrolyzer composed of two symmetrical CoP NW electrodes can deliver 10 and 100 mA cm-2 at low cell voltages of 1.56 and 1.78 V, respectively. The CoP NW electrolyzer demonstrates exceptional long-term stability for overall water splitting, capable of working at 20 and 100 mA cm-2 for 1000 h without obvious degradation.

Alkaline water electrolysis produces H2 gas, which can be used as a fuel in H2/O2 fuel cells to generate power. The most energy intensive step in water electrolysis is the evolution of O2 due to the large anodic overpotential of the Oxygen Evolution Reaction (OER).1 Thus, understanding and optimizing electrocatalysts for OER remains one of the grand challenges for both physical electrochemistry and energy science. For the OER in alkaline media, the best performing electrocatalysts are thermally prepared RuO2 and IrO2, which exhibit the lowest OER overpotentials to date, but these oxides are expensive and somewhat unstable in alkaline media, rendering them impractical and uneconomical.1 First row Transition Metal Oxides (TMO), e.g. Mn, Ni, Co or Fe, show great promise as alternative materials for OER, as they exhibit low overpotentials and high stability at lower costs than those of RuO2 or IrO2. However, mechanistic studies of OER at TMO electrodes in alkaline media have been sparse and the nature of catalytic sites and the mechanism leading to O2 evolution are not well understood.2 In this work, pure and mixed Ni/Fe materials were electrochemically deposited on Ti supports to fabricate inexpensive electrocatalysts. Their potential as OER catalysts was elucidated in NaOH electrolyte with different amounts of Fe impurities; 1 ppb, 5 ppb and 102 ppb, as determined by Inductive Coupled Plasma (ICP) spectroscopy. The results indicate that the electrocatalytic activity of the materials depends on the ratio of Ni/Fe and the concentration of Fe impurities in the electrolyte. Most of the mixed catalysts show improved OER performances compared to the pure Ni and Fe oxide materials with respect to overpotential at 10 mA cm-2, Figure 1(a), Tafel slope values and Turnover Frequencies (TOF) numbers. Interestingly, the pure and mixed Ni/Fe materials in the NaOH electrolyte containing 5 ppb Fe impurities exhibited lower overpotentials at 10mA cm-2 compared to the same material in the NaOH containing 1 ppb and 100 ppb, Figure 1(a). This is thought to be due to the substitution of the Fe ions in the electrolyte for the Ni atoms in the material lattice, improving the OER performance.3 Pure and mixed manganese and ruthenium oxides were also examined in this work. The OER catalytic activity of pure manganese oxide compounds displaying overpotentials between 0.74 - 0.49 V at a current density of 10 mA cm-2. Furthermore, when combined with other compounds this overpotential value further decreases.4 However, mechanistic studies of the OER at thermally prepared DSA® type MnxOy electrodes in alkaline media have been sparse.2 Several of the mixed Mn/Ru electrode materials in this study were found to exhibit significantly improved OER activity and stability when compared with pure RuO2films, Figure 1(b), while lowering the cost of producing the catalyst.5 These Mn/Ru materials could therefore offer a competitive low-cost alternative to the already commercially available OER catalysts. The composition, morphology and structure of all the aforementioned materials are thoroughly characterised by X-Ray Photoelectron Spectroscopy (XPS), Raman spectroscopy and Scanning Electron Microscopy–Energy Dispersive X-Ray (SEM-EDX). Finally, the Ni/Fe and Mn/Ru oxides will be a compared under cost and OER performance, to help identify the most economic and practical OER catalyst in this work. Acknowledgements We would like to thank Science Foundation Ireland (SFI) under the Grant Number SFI/10/IN.1/I2969. References (1) Lyons, M. E. G.; Doyle, R. L.; Fernandez, D.; Godwin, I. J.; Browne, M. P.; Rovetta, A. Electrochem. Commun. 2014, 45, 56-59. (2) Fernández, J. L.; Gennero De Chialvo, M. R.; Chialvo, A. C. J. Appl. Electrochem. 2002, 32, 513-520. (3) Klaus, S.; Louie, M. W.; Trotochaud, L.; Bell, A. T. The Journal of Physical Chemistry C 2015, 119, 18303-18316. (4) Gao, M.-R.; Xu, Y.-F.; Jiang, J.; Zheng, Y.-R.; Yu, S.-H. J. Am. Chem. Soc. 2012, 134, 2930-2933. (5) Browne, M. P.; Nolan, H.; Duesberg, G. S.; Colavita, P. E.; Lyons, M. E. G. ACS Catalysis 2016. Figure 1

Designing well-defined nanointerfaces is of prime importance to enhance the activity of nanoelectrocatalysts for different catalytic reactions. However, studies on non-noble-metal-interface electrocatalysts with extremely high activity and superior stability at high current density still remains a great challenge. Herein, a class of Co3 O4 /Fe0.33 Co0.66 P interface nanowires is rationally designed for boosting oxygen evolution reaction (OER) catalysis at high current density by partial chemical etching of Co(CO3 )0.5 (OH)·0.11H2 O (Co-CHH) nanowires with Fe(CN)6 3- , followed by low-temperature phosphorization treatment. The resulting Co3 O4 /Fe0.33 Co0.66 P interface nanowires exhibit very high OER catalytic performance with an overpotential of only 215 mV at a current density of 50 mA cm-2 and a Tafel slope of 59.8 mV dec-1 in 1.0 m KOH. In particular, Co3 O4 /Fe0.33 Co0.66 P exhibits an obvious advantage in enhancing oxygen evolution at high current density by showing an overpotential of merely 291 mV at 800 mA cm-2 , much lower than that of RuO2 (446 mV). Co3 O4 /Fe0.33 Co0.66 P is remarkably stable for the OER with negligible current loss under overpotentials of 200 and 240 mV for 150 h. Theoretical calculations reveal that Co3 O4 /Fe0.33 Co0.66 P is more favorable for the OER since the electrochemical catalytic oxygen evolution barrier is optimally lowered by the active Co- and O-sites from the Co3 O4 /Fe0.33 Co0.66 P interface.

Transition metal-based materials are promising not only in energy storage devices such as batteries, supercapacitors, fuel cells, but also in the field of catalysis. Increasing attention is paid to push the limits of energy storage and conversion by the delicate design of nanomaterials. To this end, metal-organic-frameworks (MOFs) based materials are emerging as outstanding templates and precursors to create nanostructures with various promising functionalities, such as excellent chemical and mechanical stabilities, large specific surface areas, and adjustable pore structures, which are promising for the applications towards energy-related applications. The research work presented in this project focuses on the rational design and synthesis of MOF-derived materials with the desired structure and composition as well as their electrochemical applications. The main results and findings are summarized as follows. 1. Co-Fe alloy@N-doped carbon hollow spheres are designed and synthesized through a dual-MOF-assisted pyrolysis approach for electrocatalytic oxygen reduction reaction (ORR). In this case, dual MOFs shell and polystyrene core are coupled together by one-step encapsulation procedure, enabling the further alloying of metal centers during the pyrolysis stage. After the thermal treatment in N2, the Co-Fe alloy particles originated from the conjunct ZIF-67, and MIL-101 are homogeneously distributed and serve as active sites in porous N-doped carbon nanoshells with nanometer precision. Benefiting from the rich active sites and porous conductive matrix, the catalyst exhibited an enhanced ORR performance with a half-wave potential (E1/2) at 0.854 V. 2. A series of hollow hierarchical nanoplates (NPs) assembled by Co3O4 nanosheets doped with 13 metal atoms are developed through a cooperative etching-coordination-reorganization method for electrocatalytic oxygen evolution reaction (OER). Novel two-dimensional ZIF-67 NPs are synthesized as templates to receive a Lewis acid etching and metal species coordination to form unique cross channels, and thus further converted to hollow Co3O4 hierarchical NPs constructed from ultrathin nanosheet subunits through a controllable solvothermal reaction, during which the metal species are doped into Co3O4 crystal lattice. Benefiting from the structural and compositional advantages, the as-derived Fe-doped Co3O4 hierarchical NPs manifest superior electrocatalytic activity towards OER with an overpotential of 262 mV at 10 mA cm-2, a Tafel slope of 43 mV dec-1, and excellent stability over 50 h at 100 mA cm-2. 3. Ultrafine Pt-Co alloy nanoparticles (sub-10 nm) attached on the inner and outer shells of porous nitrogen-doped carbon nanotubes (NCNT) are synthesized through a MOF-assisted pyrolysis-replacement-reorganization method. During the thermal reorganization, the migration of Pt-Co nano-alloys to both surfaces ensures the maximized exposure of active sites while maintaining the robust attachment to the porous carbon matrix. Density functional theory calculations suggest a nearly thermodynamically-neutral free energy of adsorption of hydrogen intermediates and diversified active sites induced by alloying, thus resulting in a great promotion in intrinsic activity towards the hydrogen evolution reaction (HER). Benefiting from the delicate structural design and compositional modulation, the optimized Pt3Co@NCNT electrocatalyst manifests outstanding HER activity and superior stability in both acidic and alkaline media.