Rational design of Pt-Ni-Co ternary alloy nanoframe crystals as highly efficient catalysts toward the alkaline hydrogen evolution reaction

Synergizing ternary CoMoW alloy with CeO2 for enhancing electrocatalytic hydrogen evolution

Integrating metal materials with metal oxides to construct a multi-component electrocatalyst represents an effective strategy to develop high-performance electrocatalysts for hydrogen evolution reaction (HER). In this work, we design and synthesize a synergistic heterogeneous electrocatalyst comprising of CoMoW ternary metal alloys and ceria (CeO2) nanosheet supported on nickel foam (NF) via a facile and fast electrodeposition method. The strong electronic interaction between CoMoW and CeO2 not only improves charge transfer but also promotes water dissociation and optimizes hydrogen adsorption capability, thereby improving the kinetics of HER. Benefiting from this properly designed interface, the optimized CoMoW-CeO2/NF delivered a low overpotential of only 35.25 mV at 10 mA cm-2 for HER, which is superior to many reported similar catalysts. This work offers an effective approach for the design and construction of high-performance heterogeneous electrocatalyst comprising of ternary alloys and metal oxides.

Rapid Preparation of Platinum Catalyst in Low-Temperature Molten Salt Using Microwave Method for Formic Acid Catalytic Oxidation Reaction

In this paper, platinum nanoparticles with a size of less than 50 nm were rapidly and successfully synthesized in low-temperature molten salt using a microwave method. The morphology and structure of the product were characterized by SEM, TEM, EDX, XRD, etc. The TEM and SEM results showed that the prepared product was a nanostructure with concave and uniform size. The EDX result indicated that the product was pure Pt, and the XRD pattern showed that the diffraction peaks of the product were consistent with the standard spectrum of platinum. The obtained Pt/C nanoparticles exhibited remarkable electrochemical performance in a formic acid catalytic oxidation reaction (FAOR), with a peak mass current density of 502.00 mA·mg-1Pt and primarily following the direct catalytic oxidation pathway. In addition, in the chronoamperometry test, after 24 h, the mass-specific activity value of the Pt concave NPs/C catalyst (10.91 mA·mg-1Pt) was approximately 4.5 times that of Pt/C (JM) (2.35 mA·mg-1Pt). The Pt/C NPs exhibited much higher formic acid catalytic activity and stability than commercial Pt/C. The microwave method can be extended to the preparation of platinum-based alloys as well as other catalysts.

Vanadium MXenes materials for next-generation energy storage devices

Batteries and supercapacitors have emerged as promising candidates for next-generation energy storage technologies. The rapid development of new two-dimensional (2D) electrode materials indicates a new era in energy storage devices. MXenes are a new type of layered 2D transition metal carbides, nitrides, or carbonitrides that have drawn much attention because of their excellent electrical conductivity, electrochemical and hydrophilic properties, large surface area, and attractive topological structure. This review focuses on various synthesis methods to prepare vanadium carbide MXenes with and without etchants like hydrofluoric acid, lithium fluoride, and hydrochloric acid to remove the 'A' layers of the MAX phase. The goal is to demonstrate the utilization of a less toxic etching method to achieve MXenes of comparable properties to those prepared by traditional methods. The influence of intercalation on the effect of high interlayer spacing between the MXene layers and the performance of MXenes as supercapacitor and battery electrodes is also addressed in this review. Lastly, the gaps in the current knowledge for vanadium carbide MXenes in synthesis, scalability, and utilization in more energy storage devices were discussed.

Recent Advances in Anode Electrocatalysts for Direct Formic Acid Fuel Cells - Part I - Fundamentals and Pd Based Catalysts

Direct formic acid fuel cells (DFAFCs) have gained immense importance as a source of clean energy for portable electronic devices. It outperforms other fuel cells in several key operational and safety parameters. However, slow kinetics of the formic acid oxidation at the anode remains the main obstacle in achieving a high power output in DFAFCs. Noble metal-based electrocatalysts are effective, but are expensive and prone to CO poisoning. Recently, a substantial volume of research work have been dedicated to develop inexpensive, high activity and long lasting electrocatalysts. Herein, recent advances in the development of anode electrocatalysts for DFAFCs are presented focusing on understanding the relationship between activity and structure. This review covers the literature related to the electrocatalysts based on noble metals, non-noble metals, metal-oxides, synthesis route, support material, and fuel cell performance. The future prospects and bottlenecks in the field are also discussed at the end.

Emerging carbon shell-encapsulated metal nanocatalysts for fuel cells and water electrolysis

The development of low-cost, high-efficiency electrocatalysts is of primary importance for hydrogen energy technology. Noble metal-based catalysts have been extensively studied for decades; however, activity and durability issues still remain a challenge. In recent years, carbon shell-encapsulated metal (M@C) catalysts have drawn great attention as novel materials for water electrolysis and fuel cell applications. These electrochemical reactions are governed mainly by interfacial charge transfer between the core metal and the outer carbon shell, which alters the electronic structure of the catalyst surface. Furthermore, the rationally designed and fine-tuned carbon shell plays a very interesting role as a protective layer or molecular sieve layer to improve the performance and durability of energy conversion systems. Herein, we review recent advances in the use of M@C type nanocatalysts for extensive applications in fuel cells and water electrolysis with a focus on the structural design and electronic structure modulation of carbon shell-encapsulated metal/alloys. Finally, we highlight the current challenges and future perspectives of these catalytic materials and related technologies in this field.

One-Step Microwave-Assisted Synthesis of PtNiCo/rGO Electrocatalysts with High Electrochemical Performance for Direct Methanol Fuel Cells

Platinum (Pt) is widely used as an activator in direct methanol fuel cells (DMFCs). However, the development of Pt catalyst is hindered due to its high cost and CO poisoning. A multi-metallic catalyst is a promising catalyst for fuel cells. We develop a simple and rapid method to synthesize PtNiCo/rGO nanocomposites (NCs). The PtNiCo/rGO NCs catalyst was obtained by microwave-assisted synthesis of graphene oxide (GO) with Pt, Ni, and Co precursors in ethylene glycol (EG) solution after heating for 20 min. The Pt-Ni-Co nanoparticles showed a narrow particle size distribution and were uniformly dispersed on the reduced graphene oxide without agglomeration. Compared with PtNiCo catalyst, PtNiCo/rGO NCs have superior electrocatalytic properties, including a large electrochemical active surface area (ECSA), the high catalytic activity of methanol, excellent anti-toxic properties, and high electrochemical stability. The ECSA can be up to 87.41 m2/g at a scan rate of 50 mV/s. They also have the lowest oxidation potential of CO. These excellent electrochemical performances are attributed to the uniform dispersion of PtNiCo nanoparticles, good conductivity, stability, and large specific surface area of the rGO carrier. The synthesized PtNiCo/rGO nanoparticles have an average size of 17.03 ± 1.93 nm. We also investigated the effect of catalyst material size on electrocatalytic performance, and the results indicate that PtNiCo/rGO NC catalysts can replace anode catalyst materials in fuel cell applications in the future.

Recent progress in water-splitting electrocatalysis mediated by 2D noble metal materials

Two-dimensional (2D) nanostructures have enabled noble-metal-based nanomaterials to be promising electrocatalysts toward overall water splitting due to their inherent structural advantages, including a high specific surface active area, numerous low-coordinated atoms, and a high density of defects and edges. Moreover, it is also disclosed that the electronic effect and strain effect within 2D nanostructures also benefit the further promotion of the electrocatalytic performance. In this review, we have focused on the recent progress in the fabrication of advanced electrocatalysts based on 2D noble-metal-based nanomaterials toward water splitting electrocatalysis. First, fundamental descriptions about water-splitting mechanisms, some promising engineering strategies, and major challenges in electrochemical water splitting are given. Then, the structural merits of 2D nanostructures for water splitting electrocatalysis are also highlighted, including abundant surface active sites, lattice distortion, abundant surface defects, electronic effects, and strain effects. Additionally, some representative water-splitting electrocatalysts have been discussed in detail to highlight the superiorities of 2D noble-metal-based nanomaterials for electrochemical water splitting. Finally, the underlying challenges and future opportunities for the fabrication of more advanced electrocatalysts for water splitting are also highlighted. We hope that this review article provides guidance for the fabrication of more efficient electrocatalysts for boosting industrial hydrogen production via water splitting.

Heteroatom-Doping of Non-Noble Metal-Based Catalysts for Electrocatalytic Hydrogen Evolution: An Electronic Structure Tuning Strategy

Electrocatalytic water splitting for hydrogen production is an appealing way to reduce carbon emissions and generate renewable fuels. This promising process, however, is limited by its sluggish reaction kinetics and high-cost catalysts. Construction of low-cost and high-performance non-noble metal-based catalysts have been one of the most effective approaches to address these grand challenges. Notably, the electronic structure tuning strategy, which could subtly tailor the electronic states, band structures, and adsorption ability of the catalysts, has become a pivotal way to further enhance the electrochemical water splitting reactions based on non-noble metal-based catalysts. Particularly, heteroatom-doping plays an effective role in regulating the electronic structure and optimizing the intrinsic activity of the catalysts. Nevertheless, the reaction kinetics, and in particular, the functional mechanisms of the hetero-dopants in catalysts yet remains ambiguous. Herein, the recent progress is comprehensively reviewed in heteroatom doped non-noble metal-based electrocatalysts for hydrogen evolution reaction, particularly focus on the electronic tuning effect of hetero-dopants in the catalysts and the corresponding synthetic pathway, catalytic performance, and activity origin. This review also attempts to establish an intrinsic correlation between the localized electronic structures and the catalytic properties, so as to provide a good reference for developing advanced low-cost catalysts.

Recent Progress of Ultrathin 2D Pd-Based Nanomaterials for Fuel Cell Electrocatalysis

Pd- and Pd-based catalysts have emerged as potential alternatives to Pt- and Pt-based catalysts for numerous electrocatalytic reactions, particularly fuel cell-related reactions, including the anodic fuel oxidation reaction (FOR) and cathodic oxygen reduction reaction (ORR). The creation of Pd- and Pd-based architectures with large surface areas, numerous low-coordinated atoms, and high density of defects and edges is the most promising strategy for improving the electrocatalytic performance of fuel cells. Recently, 2D Pd-based nanomaterials with single or few atom thickness have attracted increasing interest as potential candidates for both the ORR and FOR, owing to their remarkable advantages, including high intrinsic activity, high electron mobility, and straightforward surface functionalization. In this review, the recent advances in 2D Pd-based nanomaterials for the FOR and ORR are summarized. A fundamental understanding of the FOR and ORR is elaborated. Subsequently, the advantages and latest advances in 2D Pd-based nanomaterials for the FOR and ORR are scientifically and systematically summarized. A systematic discussion of the synthesis methods is also included which should guide researchers toward more efficient 2D Pd-based electrocatalysts. Lastly, the future outlook and trends in the development of 2D Pd-based nanomaterials toward fuel cell development are also presented.

NiAg0.4 3D porous nanoclusters with epitaxial interfaces exhibiting Pt like activity towards hydrogen evolution in alkaline medium

The necessity of Earth-abundant low-cost catalysts with activity similar to noble metals such as platinum is indispensable in order to realize the production of hydrogen through electrolysis of water. Herein, we report a relatively low-cost NiAg_0.4 3D porous nanocluster catalyst whose activity matches with that of the state-of-the-art Pt/C in 1 M KOH solution. The catalyst is designed on the principle of creating an interface between a metal having a positive Gibbs energy of hydrogen adsorption and a metal of negative Gibbs energy based on the volcano plot, to tune the Gibbs energy of hydrogen adsorption near zero for enhanced hydrogen evolution. The synthesized NiAg_0.4 3D porous nanoclusters are comprised of nanoparticles of lateral dimension ∼50 nm forming a 3D porous network with pores of 10 nm-80 nm. A high-resolution transmission electron microscopy image reveals the epitaxial growth of Ag (200) on the Ni (111) plane leading to the creation of abundant interfaces between the Ni and Ag lattices. The catalyst needs a low overpotential of 40 mV@10 mA cm^-2 with a Tafel slope of 39.1 mV dec^-1 in 1 M KOH solution. Furthermore, the catalyst exhibits a high specific activity of 0.1 mA cm^-2_(ECSA) at an overpotential (η) of 45 mV which matches with the specific activity of Pt/C 20% wt. catalyst (0.1 mA cm^-2@η = 26 mV). Density functional theory calculations reveal that the Ni-Ag interface furnishes a pathway with a reduced Gibbs energy of adsorption of -0.04 eV, thus promoting enhanced hydrogen evolution. In summary, this study reveals excellent HER activity at the Ni-Ag interface.

Low Pt-Content Ternary PtNiCu Nanoparticles with Hollow Interiors and Accessible Surfaces as Enhanced Multifunctional Electrocatalysts

Developing highly active and durable electrocatalysts with low levels of Pt content toward some crucial reactions including oxygen reduction reaction, hydrogen evolution reaction, and methanol oxidation reaction in an acidic electrolyte environment are desirable but still an open challenge for clean and efficient energy conversion. Herein, we present a facile route to synthesize low Pt-content ternary PtNiCu nanostructures with hollow interior and accessible surfaces (H-PtNiCu-AAT NPs) as enhanced multifunctional electrocatalysts. The galvanic replacement reaction and atomic diffusion between in situ preformed CuNi nanocrystals and Pt species should be responsible for the formation of hollow PtNiCu NPs. Continuous activation by acid picking and annealing treatments were performed to leach out the excessive Cu and Ni on the surfaces and to enrich Pt-content on the surface. H-PtNiCu-AAT NPs exhibit excellent activity and durability toward HER, ORR, and MOR due to the rational integration of multiple structural advantages. Strikingly, the mass activity and specific activity of H-PtNiCu-AAT NPs (0.977 A mg_Pt^-1 and 1.458 mA cm^-2) is 7.1 and 6.9 times higher than that of commercial Pt/C (0.138 A mg_Pt^-1 and 0.212 mA cm^-2) toward ORR at 0.9 V (vs RHE), respectively. This present work provides an efficient strategy for the design of low Pt-content trimetallic electrocatalysts with excellent activity and durability.

Cu- and Fe-Codoped Ni Porous Networks as an Active Electrocatalyst for Hydrogen Evolution in Alkaline Medium

Highly active catalysts from the earth-abundant metals are essential to materialize the low-cost production of hydrogen through water splitting. Herein, nickel porous networks codoped with Cu and Fe prepared by thermal reduction of presynthesized Cu, Fe-codoped Ni(OH)₂ nanowires are reported. The sample consists of nanoparticles of ∼80 nm, which form highly porous network clusters of ∼1 μm with a pore size of 10-100 nm. Among the various doped compositions, the NiCu_0.05Fe_0.025 porous network exhibits the best catalytic activity with a low overpotential of 60 mV for a hydrogen evolution reaction (HER) in 1 M KOH solution and a specific activity of 0.1 mA cm^-2 at 117 mV overpotential calculated based on the electrochemical active surface area (ECSA). The density functional theory calculations reveal that codoping of Fe and Cu into the Ni lattice results in a shift of d-bands of nickel to lower energy levels and thus in the reduced hydrogen adsorption energy (ΔG_H = -0.131 eV), which is close to ΔG_H for Pt (-0.09 eV). When NiCu_0.05Fe_0.025(OH)₂ nanowires is used as an oxygen evolution reaction (OER) catalyst and is coupled with NiCu_0.05Fe_0.025 porous networks for overall water splitting, the NiCu_0.05Fe_0.025∥NiCu_0.05Fe_0.025(OH)₂ catalyst couple achieves a current density of 10 mA cm^-2 at 1.491 V, similar to that of the Pt/C∥RuO₂ couple and offers a negligible loss in the performance when operated at 20 mA cm^-2 for 30 h.

Platinum nanoparticles on defect-rich nitrogen-doped hollow carbon as an efficient electrocatalyst for hydrogen evolution reactions

Design and synthesis of efficient electrocatalysts with low usage of precious metal and of high stability are essential for their practical applications in hydrogen evolution reactions. In this work, we synthesize an electrocatalyst through the deposition of platinum nanoparticles on defect-rich nitrogen-doped hollow carbon derived from surface-attached poly(4-vinylpyridine) monolayers. The platinum nanoparticles with an average diameter of about 1.8 nm are well dispersed on the outer surface of the pre-synthesized carbon material and the platinum loading is about 8.6 wt%. The mass activity of the as-synthesized catalyst under an overpotential of 55 mV is about 5.0 A mg_Pt⁻¹, about 4.93 times higher than that of commercial Pt/C catalysts. Moreover, the synthesized catalyst is also more electrochemically stable than commercial Pt/C catalysts as evidenced by continuous cyclic voltammetry and chronoamperometric response measurements.

Design and synthesis of efficient electrocatalysts with low usage of precious metal and of high stability are essential for hydrogen evolution reaction in their practical applications.

Co–Pt bimetallic nanoparticles with tunable magnetic and electrocatalytic properties prepared by atomic layer deposition

Magnetism tuning and hydrogen evolution reaction activity optimization can be achieved for Co–Pt BMNPs prepared by ALD.

A novel strategy for the synthesis of hollow Pt–Cu tetradecahedrons as an efficient electrocatalyst toward methanol oxidation

Pt–Cu TNs can be simply achieved within a few minutes by an H⁺-assisted disproportionation reaction using Cu₂O tetradecahedrons as the template. Due to its unique structural advantages, these Pt–Cu TNs exhibit extraordinary electrocatalytic performance toward MOR.

RuOx-decorated multimetallic hetero-nanocages as highly efficient electrocatalysts toward the methanol oxidation reaction

Direct methanol fuel cell technology awaits the development of highly efficient and robust nanocatalysts driving the methanol oxidation reaction (MOR) in a CO poisoning-free fashion. Thus far, various Pt-based alloy nanoparticles have been studied as electrocatalysts toward the MOR, and it has been found that the introduction of dopants such as Ru and Cu to Pt has been particularly successful in mitigating the CO poisoning problem. Herein, we report a facile synthesis of Ru-branched RuPtCu nanocages that involves in situ formation of Ru-doped PtCu nanoparticles and subsequent outgrowth of Ru branches by insertion of additional Ru precursors. We show that the electrocatalytic activity and stability of Ru branched RuPtCu ternary nanocages toward the MOR are greatly improved compared to those of PtCu/C and RuPtCu/C counterparts and state-of-the-art PtRu/C and Pt/C catalysts, mainly due to the synergy between the CO-tolerant RuO_x phase and the highly open and robust RuPtCu nanoframe.

Hollow nanoparticles as emerging electrocatalysts for renewable energy conversion reactions

While the realization of clean and sustainable energy conversion systems primarily requires the development of highly efficient catalysts, one of the main issues had been designing the structure of the catalysts to fulfill minimum cost as well as maximum performance. Until now, noble metal-based nanocatalysts had shown outstanding performances toward the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). However, the scarcity and high cost of them impeded their practical use. Recently, hollow nanostructures including nanocages and nanoframes had emerged as a burgeoning class of promising electrocatalysts. The hollow nanostructures could expose a high proportion of active surfaces while saving the amounts of expensive noble metals. In this review, we introduced recent advances in the synthetic methodologies for generating noble metal-based hollow nanostructures based on thermodynamic and kinetic approaches. We summarized electrocatalytic applications of hollow nanostructures toward the ORR, OER, and HER. We next provided strategies that could endow structural robustness to the flimsy structural nature of hollow structures. Finally, we concluded this review with perspectives to facilitate the development of hollow nanostructure-based catalysts for energy applications.

Recent advances in electrocatalysts toward the oxygen reduction reaction: the case of PtNi octahedra

Designing highly efficient and durable electrocatalysts for the oxygen reduction reaction (ORR), the key step for the operation of polymer electrolyte membrane fuel cells (PEMFCs), is of a pivotal importance for advancing PEMFC technology. Since the most significant progress has been made on Pt3Ni(111) alloy surfaces, nanoscale PtNi alloy octahedra enclosed by (111) facets have emerged as promising electrocatalysts toward the ORR. However, because their practical uses have been hampered by the cost, sluggish reaction kinetics, and poor durability, recent advances have engendered a wide variety of structure-, size-, and composition-controlled bimetallic PtNi octahedra. Herein, we therefore review the important recent developments of PtNi octahedral electrocatalysts point by point to give an overview of the most promising strategies. Specifically, the present review article focuses on the synthetic methods for the PtNi octahedra, the core-shell and multi-metallic strategies for performance improvement, and their structure-, size-, and composition-control-based ORR activity. By considering the results achieved in this field, a prospect for this alloy nanocatalysts system for future sustainable energy applications is also proposed.

In-situ electrochemical activation designed hybrid electrocatalysts for water electrolysis

Developing transition metal-based electrocatalysts with rich active sites for water electrolysis plays important roles in renewable energy fields. So far, some strategies including designing nanostructures, incorporating conductive support or foreign elements have been adopted to develop efficient electrocatalysts. Herein, we summarize recent progresses and propose in-situ electrochemical activation as a new pretreating technique for enhanced catalytic performances. The activation techniques mainly comprise facile electrochemical processes such as anodic oxidation, cathodic reduction, etching, lithium-assisted tuning and counter electrode electro-dissolution. During these electrochemical treatments, the catalyst surfaces are modified from bulk phase, which can tune local electronic structures, create more active species, enlarge surface area and thus improve the catalytic performances. Meanwhile, this technique can couple the atomic, electronic structures with electrocatalysis mechanisms for water splitting. Compared to traditional chemical treatment, the in-situ electrochemical activation techniques have superior advantages such as facile operation, mild environment, variable control, high efficiency and flexibility. This review may provide guidance for improving water electrolysis efficiencies and hold promising for application in many other energy-conversion fields such as supercapacitors, fuel cells and batteries.

General Synthetic Strategy for Libraries of Supported Multicomponent Metal Nanoparticles

Nanoparticles comprising three or more different metals are challenging to prepare. General methods that tackle this challenge are highly sought after as multicomponent metal nanoparticles display favorable properties in applications such as catalysis, biomedicine, and imaging. Herein, we report a practical and versatile approach for the synthesis of nanoparticles composed of up to four different metals. This method relies on the thermal decomposition of nanostructured composite materials assembled from platinum nanoparticles, a metal-organic framework (ZIF-8), and a tannic acid coordination polymer. The controlled integration of multiple metal cations (Ni, Co, Cu, Mn, Fe, and/or Tb) into the tannic acid shell of the precursor material dictates the composition of the final multicomponent metal nanoparticles. Upon thermolysis, the platinum nanoparticles seed the growth of the multicomponent metal nanoparticles via coalescence with the metallic constituents of the tannic acid coordination polymer. The nanoparticles are supported in the walls of hollow nitrogen-doped porous carbon capsules created by the decomposition of the organic components of the precursor. The capsules prevent sintering and detachment of the nanoparticles, and their porosity allows for efficient mass transport. To demonstrate the utility of producing a broad library of supported multicomponent metal nanoparticles, we tested their electrocatalytic performance toward the hydrogen evolution reaction and oxygen evolution reaction. We discovered functional relationships between the composition of the nanoparticles and their electrochemical activity and identified the PtNiCu and PtNiCuFe nanoparticles as particularly efficient catalysts. This highlights how to generate diverse libraries of multicomponent metal nanoparticles that can be synthesized and subsequently screened to identify high-performance materials for target applications.

Dendrite-Embedded Platinum-Nickel Multiframes as Highly Active and Durable Electrocatalyst toward the Oxygen Reduction Reaction

Pt-based nanoframe catalysts have been explored extensively due to their superior activity toward the oxygen reduction reaction (ORR). Herein, we report the synthesis of Pt-Ni multiframes, which exhibit the unique structure of tightly fused multiple nanoframes and reinforced by an embedded dendrite. Rapid reduction and deposition of Ni atoms on Pt-Ni nanodendrites induce the alloying/dealloying of Pt and Ni in the overall nanostructures. After chemical etching of Ni, the newly formed dendrite-embedded Pt-Ni multiframes show an electrochemically active surface area (ECSA) of 73.4 m² g_Pt^-1 and a mass ORR activity of 1.51 A mg_Pt^-1 at 0.93 V, which is 30-fold higher than that of the state-of-the-art Pt/C catalyst. We suggest that high ECSA and ORR performances of dendrite-embedded Pt-Ni multiframes/C can be attributed to the porous nanostructure and numerous active sites exposed on surface grain boundaries and high-indexed facets.

Molybdenum Carbide-Decorated Metallic Cobalt@Nitrogen-Doped Carbon Polyhedrons for Enhanced Electrocatalytic Hydrogen Evolution

Electrocatalytic hydrogen evolution reaction (HER) based on water splitting holds great promise for clean energy technologies, in which the key issue is exploring cost-effective materials to replace noble metal catalysts. Here, a sequential chemical etching and pyrolysis strategy are developed to prepare molybdenum carbide-decorated metallic cobalt@nitrogen-doped porous carbon polyhedrons (denoted as Mo/Co@N-C) hybrids for enhanced electrocatalytic hydrogen evolution. The obtained metallic Co nanoparticles are coated by N-doped carbon thin layers while the formed molybdenum carbide nanoparticles are well-dispersed in the whole Co@N-C frames. Benefiting from the additionally implanted molybdenum carbide active sites, the HER performance of Mo/Co@N-C hybrids is significantly promoted compared with the single Co@N-C that is derived from the pristine ZIF-67 both in alkaline and acidic media. As a result, the as-synthesized Mo/Co@N-C hybrids exhibit superior HER electrocatalytic activity, and only very low overpotentials of 157 and 187 mV are needed at 10 mA cm^-2 in 1 m KOH and 0.5 m H₂ SO₄ , respectively, opening a door for rational design and fabrication of novel low-cost electrocatalysts with hierarchical structures toward electrochemical energy storage and conversion.

Monocrystalline platinum-nickel branched nanocages with enhanced catalytic performance towards the hydrogen evolution reaction

Single crystalline noble metal nanocages are the most promising candidates for heterogeneous catalysis due to their large specific surface area, well-defined structure and enhanced structural stability. Herein, based on the observation of an unexpected phenomenon that the alloying of Pt and transition metals by co-reduction is more preferential than the formation of pure Pt NCs, we propose a feasible one-pot strategy to synthesize a uniformly epitaxial core-shell Pt-Ni structure with a Ni-rich alloy as the core and a Pt-rich alloy as the shell. The as-prepared Pt-Ni core-shell structures are subsequently etched into monocrystalline Pt-Ni branched nanocages with the wall thickness being 2.8 nm. This unique structure exhibits excellent catalytic performance and stability for the hydrogen evolution reaction (HER) in alkaline solution which is of great significance for the energy-intensive water-alkali and chlor-alkali industry.

Electrocatalysts for Hydrogen Evolution in Alkaline Electrolytes: Mechanisms, Challenges, and Prospective Solutions

Hydrogen evolution reaction (HER) in alkaline medium is currently a point of focus for sustainable development of hydrogen as an alternative clean fuel for various energy systems, but suffers from sluggish reaction kinetics due to additional water dissociation step. So, the state-of-the-art catalysts performing well in acidic media lose considerable catalytic performance in alkaline media. This review summarizes the recent developments to overcome the kinetics issues of alkaline HER, synthesis of materials with modified morphologies, and electronic structures to tune the active sites and their applications as efficient catalysts for HER. It first explains the fundamentals and electrochemistry of HER and then outlines the requirements for an efficient and stable catalyst in alkaline medium. The challenges with alkaline HER and limitation with the electrocatalysts along with prospective solutions are then highlighted. It further describes the synthesis methods of advanced nanostructures based on carbon, noble, and inexpensive metals and their heterogeneous structures. These heterogeneous structures provide some ideal systems for analyzing the role of structure and synergy on alkaline HER catalysis. At the end, it provides the concluding remarks and future perspectives that can be helpful for tuning the catalysts active-sites with improved electrochemical efficiencies in future.

Ni3[Fe(CN)6]2 nanocubes boost the catalytic activity of Pt for electrochemical hydrogen evolution

Hybrid electrocatalyst of ultrafine Pt particles anchored on a Ni₃[Fe(CN)₆]₂ nanocube with low Pt loading of 4.0% is designed for HERs, and superior catalytic activity is obtained in both acidic and alkaline media because the Ni species remarkably facilitates the reaction kinetics of water dissociation and thus improves HER activity.

Ferric phosphide carbon nanocomposites emerging as highly active electrocatalysts for the hydrogen evolution reaction

This Frontier article highlights the recent development and advances in designing ferric phosphide (FeP) based composite materials for the HER.

Superior alkaline hydrogen evolution electrocatalysis enabled by an ultrafine PtNi nanoparticle-decorated Ni nanoarray with ultralow Pt loading

An ultrafine PtNi nanoparticle-decorated Ni nanosheet array with ultralow Pt loading acts as a superior hydrogen-evolving electrocatalyst.

Radially Phase Segregated PtCu@PtCuNi Dendrite@Frame Nanocatalyst for the Oxygen Reduction Reaction

Pt-based alloy nanoframes have shown great potential as electrocatalysts toward the oxygen reduction reaction (ORR) in fuel cells. However, the intrinsically infirm nanoframes could be severely deformed during extended electro-cyclings, which eventually leads to the loss of the initial catalytic activity. Therefore, the structurally robust nanoframe is a worthy synthetic target. Furthermore, ternary alloy phase electrocatalysts offer more opportunities in optimizing the stability and activity than binary alloy ones. Herein, we report a robust PtCuNi ternary nanoframe, structurally fortified with an inner-lying PtCu dendrite, which shows a highly active and stable catalytic performance toward ORR. Remarkably, the PtCu@PtCuNi catalyst exhibited 11 and 16 times higher mass and specific activities than those of commercial Pt/C.

Pt nanocrystals on nitrogen-doped graphene for the hydrogen evolution reaction using Si nanowires as a sacrificial template

Cost-effective catalysts for electrocatalytic water splitting play a key role in the renewable energy research. Although Pt has been regarded as the best catalyst, its wide applications have been impeded by its high cost and scarce natural abundance. Therefore, decreasing the Pt usage for electrocatalyst design is significant toward the hydrogen evolution reaction (HER). Herein, flower-like Pt nanocrystals were loaded on the surface of nitrogen-doped graphene using Si nanowires as the sacrificial template. The experimental results showed that the optimal Pt nanocrystals/N-doped graphene with superior HER activity and excellent stability only has a low Pt loading of 5.0 wt%. It is noted that the HER mass activity of the Pt nanocrystals/N-doped graphene is 5 fold higher than that of the 20.0 wt% Pt/C commercial catalyst. This optimal catalyst also achieved a low Tafel slope (28.0 mV dec^-1), large apparent exchange current density (0.989 mA cm^-2) and high turnover frequency (2.05 s^-1). This work may provide an effective avenue for developing highly efficient electrochemical catalysts for the HER.

In Situ Synthesis Strategy for Hierarchically Porous Ni2P Polyhedrons from MOFs Templates with Enhanced Electrochemical Properties for Hydrogen Evolution

The development of highly active and stable noble metal-free electrocatalysts of hydrogen evolution reaction (HER) under both acidic and basic conditions for renewable-energy conversion techniques is of great significance. Herein, a practical in situ synthesis strategy for a three-dimensional Ni₂P polyhedron with a hierarchically porous structure was presented, which was efficiently obtained from a nickel centered metal-organic frameworks (MOF-74-Ni) by direct low-temperature phosphorization. The as-prepared Ni₂P polyhedron showed a high BET surface area (175.0 m²·g^-1), hierarchically porous property, and outstanding metal dispersion, which well inherited the morphology and porosity of its MOF precursor. Compared with Ni₂P particles obtained from a nonporous precursor, the as-prepared Ni₂P polyhedron used as electrocatalyst exhibited excellent electrocatalytic performance toward the HER, with a low overpotential of 158 mV to produce the cathodic current density of 10 mA cm^-2. A small Tafel slope of 73 mV per decade is obtained for Ni₂P polyhedron, which revealed a Volmer-Heyrovsky mechanism during the HER. In addition, benefiting from the structural stability, the porous Ni₂P polyhedron used as a electrocatalyst showed satisfactory long-term durability for the HER in acidic media.