Non-noble Metal Electrocatalysts Research Articles

Bifunctional hierarchical NiCoP@FeNi LDH nanosheet array electrocatalyst for industrial-scale high-current-density water splitting

Aiming to design and prepare non-noble metal electrocatalysts for hydrogen production at high current density (HCD), NiCoP@FeNi LDH hierarchical nanosheets were deposited on nickel foam progressively using a hydrothermal-phosphorization-electrodeposition process. For hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), NiCoP@FeNi LDH/NF requires only 195 and 230 mV overpotentials to reach 1000 mA cm−2, respectively. For overall water splitting, only 1.70 V is required at 1000 mA cm−2. This is the largest value for non-noble metal-based electrocatalysts reported so far at HCD. The hierarchical structure exhibits good electron transport capability and the porous-macroporous structure enhances the gas release rate, resulting in enhanced hydrogen production at HCD. Especially, the synergistic effect of NiCoP and FeNi LDH contributes to the adsorption-desorption equilibrium of intermediate radicals during the reaction process and ultimately enhances the catalytic activity. This work provides useful direction for industrial-scale hydrogen production applications at HCD.

Stabilization of non-noble metal electrocatalysts for acidic oxygen evolution reaction

Modern proton exchange membrane water electrolyzers rely on noble metal electrocatalysts. The application of Ir and Pt in such electrolyzers is considered a prerequisite for their long-term operation. However, the scarcity of these critical raw materials is the major drawback of this technology. In recent years, the academic community scrutinized the suitability of non-noble metals as alternative electrocatalysts. While these metals still demonstrate relatively low activity and stability, significant progress has been achieved in improving their performance. Here, we briefly overview recent achievements in oxygen evolution electrocatalysis using non-noble metals. We identify and discuss five stabilization strategies: (a) thermodynamic stabilization; (b) suppression of dissolution kinetics; (c) electrolyte engineering; (d) protection of active interfaces; and (e) system-level solutions. We provide critical remarks on the advantages and drawbacks of the strategies. Moreover, following our previous opinions in this journal, we highlight the significance of testing non-noble metal electrocatalysts in real devices.

Co Nanoparticles Confined in Mesoporous Mo/N Co-Doped Polyhedral Carbon Frameworks towards High-Efficiency Oxygen Reduction.

Exploiting effective non-noble metal electrocatalysts for oxygen reduction reaction (ORR) is crucial for fuel cells and metal-air batteries. Herein, we designed and fabricated Co nanoparticles confined in Mo/N co-doped polyhedral carbon frameworks (Co-NP/MNCF) derived from polyoxometalate-encapsuled metal-organic framework, which showed comparable ORR performance with commercial Pt/C and a larger diffusion-limited current density. Moreover, the Co-NP/MNCF also exhibited excellent ORR stability and methanol tolerance. These appealing performances can be attributed to the porosity regulation and heteroatom doping of metal-organic framework derived polyhedral carbon frameworks, which could be beneficial for the exposure of more active sites, the optimization of electronic structure and the mass transfer of electrolyte/electron/ion.

Tungsten Disulfide-Interfacing Nickel-Porphyrin For Photo-Enhanced Electrocatalytic Water Oxidation.

Covalent functionalization of tungsten disulfide (WS2 ) with photo- and electro-active nickel-porphyrin (NiP) is reported. Exfoliated WS2 interfacing NiP moieties with 1,2-dithiolane linkages is assayed in the oxygen evolution reaction under both dark and illuminated conditions. The hybrid material presented, WS2 -NiP, is fully characterized with complementary spectroscopic, microscopic, and thermal techniques. Standard yet advanced electrochemical techniques, such as linear sweep voltammetry, electrochemical impedance spectroscopy, and calculation of the electrochemically active surface area, are used to delineate the catalytic profile of WS2 -NiP. In-depth study of thin films with transient photocurrent and photovoltage response assays uncovers photo-enhanced electrocatalytic behavior. The observed photo-enhanced electrocatalytic activity of WS2 -NiP is attributed to the presence of Ni centers coordinated and stabilized by the N4 motifs of tetrapyrrole rings at the tethered porphyrin derivative chains, which work as photoreceptors. This pioneering work opens wide routes for water oxidation, further contributing to the development of non-noble metal electrocatalysts.

Interfacial Chemical Bond Modulation of Co3(PO4)2-MoO3-x Heterostructures for Alkaline Water/Seawater Splitting.

The development of a high current density with high energy conversion efficiency electrocatalyst is vital for large-scale industrial application of alkaline water splitting, particularly seawater splitting. Herein, we design a self-supporting Co3(PO4)2-MoO3-x/CoMoO4/NF superaerophobic electrode with a three-dimensional structure for high-performance hydrogen evolution reaction (HER) by a reasonable devise of possible "Co-O-Mo hybridization" on the interface. The "Co-O-Mo hybridization" interfaces induce charge transfer and generation of fresh oxygen vacancy active sites. Consequently, the unique heterostructures greatly facilitate the dissociation process of H2O molecules and enable efficient hydrogen spillover, leading to excellent HER performance with ultralow overpotentials (76 and 130 mV at 100 and 500 mA cm-2) and long-term durability of 100 h in an alkaline electrolyte. Theoretical calculations reveal that the Co3(PO4)2-MoO3-x/CoMoO4/NF promotes the adsorption/dissociation process of H2O molecules to play a crucial role in improving the stability and activity of HER. Our results exhibit that the HER activity of non-noble metal electrocatalysts can be greatly enhanced by rational interfacial chemical bonding to modulate the heterostructures.

Chromium doping and in-grown heterointerface construction for modifying Ni3FeN toward bifunctional electrocatalyst toward alkaline water splitting

Exploring high-performance non-noble metal electrocatalysts is pivotal for eco-friendly hydrogen energy applications. Herein, featuring simultaneous Chromium doping and in-grown heterointerface engineering, the Cr doping Ni3FeN/Ni heterostructure supported on N-doped graphene tubes (denoted as Cr–Ni3FeN/Ni@N-GTs) was successfully constructed, which exhibits the superior bifunctional electrocatalytic performances (88 mV and 262 mV at 10 mA cm−2 for HER and OER, respectively). Furthermore, an alkaline electrolyzer, employing Ni3FeN/Ni@N-GTs as both the cathode and the anode, requires a low cell voltage of 1.57 V at 10 mA⋅cm−2. Cr doping not only modulates the electronic structure of host Ni and Fe but also synchronously induces nitrogen vacancies, leading to a higher number of active sites; the in-grown heterointerface Cr–Ni3FeN/Ni induces the charge redistribution by spontaneous electron transfer across the heterointerface, enhancing the intrinsic catalytic activity; the N-GTs skeleton with excellent electrical conductivity improves the electron transport and mass transfer. The synergy of the above merits endows the designed Cr–Ni3FeN/Ni@ N-GTs with outstanding electrocatalytic properties for alkaline overall water splitting.

Multifunctional Amorphous Co Phosphosulfide-Coated Fe-Co Carbonate Hydroxide for Highly Efficient Overall Water Splitting

Non-noble metal electrocatalysts current represent an appealing alternative to noble metal electrocatalysts for water oxidation reaction in alkaline conditions. However, the poor water reduction reaction activities limit their performance in driving overall water splitting in alkaline electrolytes. Here, we report the preparation of bifunctional amorphous Co phosphosulfide-doped Fe-Co carbonate hydroxide on the surface of Ni foam (Co-S-P/Fe1Co1COH/NF) through hydrothermal and electrochemical techniques. The efficient full water oxidation and reduction properties of the Co-S-P/Fe1Co1COH/NF were verified in pH = 14 medium. The results proved that a phosphorus and sulfur co-depositing catalyst could exhibit excellent anodic oxidation and cathodic reduction activity for full water splitting. Furthermore, the optimal electrocatalyst can afford a current density of 10 mA cm−2 at an overpotential of only 73 mV for hydrogen evolution from water reduction and 50 mA cm−2 at 160 mV for oxygen evolution from water oxidation in 1.0 M KOH solution, showing better activities than most non-noble metal materials. The improved electrocatalytic activities could be attributed to the increased number of active sites and the synergetic cooperation in the prepared material. Additionally, the Co-S-P/Fe1Co1COH/NF catalyst as both cathode and anode only needs a voltage of 1.5 V to achieve 10 mA cm−2 in 1 M KOH solution for full water splitting, which lays a good foundation for full water splitting in practical applications.

Electrodeposition of Stable Noble-Metal-Free Co-P Electrocatalysts for Hydrogen Evolution Reaction.

Hydrogen production via water splitting has been extensively explored over the past few decades, and considerable effort has been directed toward finding more reactive and cost-effective electrocatalysts by engineering their compositions, shapes, and crystal structures. In this study, we developed hierarchical cobalt phosphide (Co-P) nanosphere assemblies as non-noble metal electrocatalysts via one-step electrodeposition. The morphologies of the Co-P nanostructures and their electrocatalytic activities towards the hydrogen evolution reactions (HER) were controlled by the applied potentials during electrodeposition. The physicochemical properties of the as-prepared Co-P nanostructures in this study were characterized by field-emission scanning electron microscopy, X-ray photoemission spectroscopy and X-ray diffraction. Linear sweep voltammetry revealed that the Co-P grown at -0.9 V showed the best HER performance exhibiting the highest electrochemical active surface area and lowest interfacial charge transfer resistance. The Co-P electrocatalysts showed superior long-term stability to electrodeposited Pt, indicating their potential benefits.

Effects of tuning the structural symmetry of cobalt porphyrin on electrocatalytic oxygen reduction reactions.

Metalloporphyrins have attracted significant attention as highly promising alternatives to Pt-based electrocatalysts in the realm of oxygen reduction reactions (ORRs). While the structure of porphyrin is widely recognized as a pivotal factor influencing the ORR performance, the impact of molecular symmetry, which is one of the key properties of the molecular structure, has rarely been understood and its effects remain largely unexplored. Herein, we designed and synthesized two triphenylamine (TPA)-substituted cobalt porphyrins, the asymmetric aBz-TCoP and the symmetric Bz-2TCoP, which are doped onto carbon black to construct composite catalysts for ORRs. The electronic structures of both porphyrins are determined through density functional theory (DFT) calculations, and the morphology and electronic states of the composites are examined by spectroscopic techniques. A series of electrochemical measurements demonstrate the superior activity, selectivity and durability of Bz-2TCoP/C to aBz-TCoP/C in ORRs conducted in both acidic and alkaline electrolytes. The improved ORR properties of the symmetric porphyrin may stem from the steric properties rather than the electronic properties of the chemical structure. This work represents a preliminary study on the effects of porphyrin structural symmetry on electrocatalysis and provides a potential strategy for further structural modifications of metalloporphyrins, as non-noble metal electrocatalysts, to enhance the ORR performance.

One-Step Construction of Co2P Nanoparticles Encapsulated into N-Doped Porous Carbon Sheets for Efficient Oxygen Evolution Reaction

It is critical and challenging to develop high performance transition metal phosphides (TMPs) electrocatalysts for oxygen evolution reaction (OER) to address fossil energy shortages. Herein, we report the synthesis of Co2P embedded in N-doped porous carbon (Co2P@N-C) via a facile one-step strategy. The obtained catalyst exhibits a lower overpotential of 352 mV for OER at a current density of 10 mA cm−2 and a small Tafel slope of 84.6 mV dec−1, with long-time reliable stability. The excellent electrocatalytic performance of Co2P@N-C can be mainly owed to the synergistic effect between the Co2P and highly conductive N-C substrate, which not only affords rich exposed active sites but also promotes faster charge transfer, thus significantly promoting OER process. This work presents a promising and industrially applicable synthetic strategy for the rational design of high performance nonnoble metal electrocatalysts with enhanced OER performance.

Insights into alloy/oxide or hydroxide interfaces in Ni-Mo-based electrocatalysts for hydrogen evolution under alkaline conditions.

Nickel-molybdenum (Ni-Mo) alloys are promising non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) in alkaline water; however, the kinetic origins of their catalytic activities still remain under debate. In this perspective, we systematically summarize the structural characteristics of Ni-Mo-based electrocatalysts recently reported and find that highly active catalysts generally have alloy-oxide or alloy-hydroxide interface structures. Based on the two-step reaction mechanism under alkaline conditions, water dissociation to form adsorbed hydrogen and combination of adsorbed hydrogen into molecular hydrogen, we discuss in detail the relationship between the two types of interface structures obtained by different synthesis methods and their HER performance in Ni-Mo based catalysts. For the alloy-oxide interfaces, the Ni4Mo/MoO x composites produced by electrodeposition or hydrothermal combined with thermal reduction exhibit activities close to that of platinum. For only the alloy or oxide, their activities are significantly lower than that of composite structures, indicating the synergistic catalytic effect of binary components. For the alloy-hydroxide interfaces, the activity of the Ni x Mo y alloy with different Ni/Mo ratios is greatly improved by constructing heterostructures with hydroxides such as Ni(OH)2 or Co(OH)2. In particular, pure alloys obtained by metallurgy must be activated to produce a layer of mixed Ni(OH)2 and MoO x on the surface to achieve high activity. Therefore, the activity of Ni-Mo catalysts probably originates from the interfaces of alloy-oxide or alloy-hydroxide, in which the oxide or hydroxide promotes water dissociation and the alloy accelerates hydrogen combination. These new understandings will provide valuable guidance for the further exploration of advanced HER electrocatalysts.

Interface engineering and heterometal-doped FeOOH/Ga-Ni3S2nanosheet arrays for efficient electrocatalytic oxygen evolution

The exploration of highly efficient and stable non-noble metal electrocatalysts for oxygen evolution reaction (OER) is a crucial challenge.

Quantum dot-doped CeOx-NiB with modulated electron density as a highly efficient bifunctional electrocatalyst for water splitting.

Development of economical, efficient and durable non-noble metal electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER) holds great promise, but still faces great challenges. Herein, a strategy of doping metal borides with rare earth metal oxides and introducing silicon carbide (SiC) quantum dots has been explored to develop efficient bifunctional electrocatalysts. A novel electrocatalyst consists of SiC quantum dot-decorated CeOx-NiB supported on nickel foam via a one-step mild electroless plating reaction (denoted as CeOx-NiB/SiC@NF). Notably, the modulated electron density of the CeOx-NiB/SiC@NF electrode significantly boosts the electrochemically active surface area and electron transfer, and optimizes the hydrogen/water absorption free energy, which delivers current densities of 50 mA cm-2 and 10 mA cm-2 at overpotentials of only 131 mV and 234 mV for the HER and the OER, respectively. The target electrode requires only 1.43 V to provide 10 mA cm-2 for overall water splitting in 1.0 M KOH. Moreover, the electrode also exhibits good stability and durability at the industrial-grade current density (0.5-1 A cm-2). This work provides a new idea for the development of efficient and durable non-precious metal catalysts.

Vanadium-induced synthesis of amorphous V-Co-P nanoparticles for an enhanced hydrogen evolution reaction.

The hydrogen evolution reaction (HER) plays a vital role for the production of pure hydrogen with zero carbon release. Developing high efficiency non-noble metal electrocatalysts could reduce its cost. Here, vanadium doped cobalt phosphide grown on carbon cloth (CC) was synthesized by the low temperature electrodeposition-phosphorization method. The influence of V dopants on the structural, morphological, and electrocatalytic performance of Vx-Co1-x-P composites was also investigated in-depth. Impressively, the optimized amorphous V0.1-Co0.9-P nano-electrocatalyst exhibits outstanding catalytic activity with a low overpotential of 50 mV at a current density of 10 mA cm-2 and a small Tafel value of 48.5 mV dec-1 in alkaline media. The results showed that V dopants in the composite change its crystal structure from the crystalline phase to the amorphous phase, resulting in the introduction of V-O sites, which regulate the electron density of the active sites and the exposure of surface active sites and thus promote the electrocatalytic HER process. This work provides a novel idea for the fabrication of high-efficiency metal phosphide based electrocatalysts.

Nano-Co-embedded carbon nanofibers for oxygen reduction reaction in Zn-air batteries

The preparation of inexpensive, environmentally friendly, and stable electro-catalysts is crucial for realizing large-scale practical applications of Zn-air batteries. Herein, Co nanoparticles are successfully encapsulated in N-doped carbon nanofibers by electrospinning technique. The obtained material has the characteristics of stable fibrous structure, abundant active centers and fast electron transport. As expected, Co@HPCNFs-800 exhibits high catalytic activity with its initial potential (0.925 V) and onset half-wave potential (0.824 V). Meanwhile, the stability of Co@HPCNFs-800 is significantly higher than commercial Pt/C. Most importantly, the rechargeable Zn-air batteries using Co@HPCNFs-800 catalyst exhibit good open-circuit voltage and cycling stability, demonstrating their potential for practical application. Therefore, this facile method can generally be used to synthesize non-noble metal electrocatalysts to improve energy conversion efficiency.

Engineering of the A-site deficiency in La0.4Sr0.6Co0.7Fe0.2Nb0.1O3-δ perovskites for enhanced elelctrocatalytic oxygen reduction reaction

• Series of (La 0.4 Sr 0.6 ) 1-x Co 0.7 Fe 0.2 Nb 0.1 O 3-δ (LSCFN) perovskites developed. • A-site deficiency enhances electrocatalytic activity for ORR in alkaline solutions. • LSCFN-0.90 with the highest density of vacant A-sites is a much better ORR catalyst. • Used as cathode in aluminum-air batteries. The development of efficient non-noble metal electrocatalysts for the oxygen reduction reaction (ORR) can aid the commercialization of fuel cells and metal-air batteries. Here, we developed a series of La 0.4 Sr 0.6 Co 0.7 Fe 0.2 Nb 0.1 O 3-δ (LSCFN) perovskites by engineering A-site deficiency to enhance their electrocatalytic activity for ORR in alkaline solutions. We found that LSCFN-0.90 with the highest amount of vacant A-sites has a highly oxidative oxygen species (O 2 2− /O − ) and an appropriate Co oxidation state - is a much better ORR catalyst in alkaline solutions compared to those with less vacant A-sites. The enhanced ORR kinetics enabled their use as the cathode catalyst in aluminum-air batteries, which also revealed better electrochemical performances for the catalyst with the highest A-site deficiency. Overall, the results demonstrate that an appropriate A-site cation deficiency in perovskites can enhance the ORR electrocatalytic activity.

Efficient electrochemical reduction of nitrate by bimetallic Cu-Fe phosphide derived from Prussian blue analogue

Designing electrocatalysts for nitrate (NO3-) reduction with excellent activity, low cost and stability is of great interest. Herein we synthesized a novel transition bimetallic phosphide (CuFeP-x, x referred to the phosphidation temperature) catalyst by phosphidation using CuFe-Prussian blue analogue (PBA) nanoparticles as the precursor. The obtained CuFeP-450 maintained the morphology of nanocube with the average size of 33.0 nm and bimetallic phosphide nanoparticles formed during the phosphidation process. The higher electrocatalytic activity of CuFeP-x in electrochemical NO3- reduction were attained as compared to that of calcined CuFe-450, because the CuFeP-x have a lower interface impedance and the dominated species for NO3- reduction changes from electron to atomic H* , which effectively enhanced the removal rate. The appropriate phosphidation temperature can form a crystal structure that facilitated reaction kinetics. As a result, CuFeP-450 showed the best electrocatalytic performance for NO3- reduction (99.42%), and the selectivity of N2 can reach nearly 100% under the condition of 1000 mg L−1 chloride ions. This simple method using PBA with binary transition metals to prepare bimetallic phosphide provides a new direction for designing efficient non-noble metal electrocatalysts for NO3- reduction.

Rare-earth metal multicomponent perovskite as a electrocatalyst for water splitting

It is urgent to exploit non-noble metal electrocatalysts for water splitting. Herein, the multicomponent perovskites containing rare-earth metals La and Y were synthesized. The as-synthesized La0.7Y0.3Co0.5Ni0.5O3 shows a low OER overpotential of 338 mV at 10 mA cm−2 and fast kinetics, which are superior to those of commercial RuO2. Moreover, the overall water splitting voltage of La0.7Y0.3Co0.5Ni0.5O3 is 1.63 V at 10 mA cm−2, which is slightly higher than that of a commercial RuO2//Pt/C system (1.60 V).

Different Growth Behavior of MOF-on-MOF Heterostructures to Enhance Oxygen Evolution.

The exploration of non-noble metal electrocatalysts with high catalytic activity and stability for oxygen evolution reaction (OER) has become particularly urgent. Here, FeNi-based Prussian blue analogues (PBAs) were obtained by adding different solvents, where PBA particles preferentially grew on the surface plane/edge of coordination polymer precursor (Ni-ABDC) with various polarities. This resulted in the formation of FeNi-PBA-plane/edge morphologies, respectively. Notably, on account of more exposed PBAs, FeNi nanoparticles were uniformly supported on the porous N-doped carbon nanomaterials. Among them, the calcined FeNi-NC-800 underwent an interesting pre-activation process and exhibited a low overpotential of 281 mV at 10 mA cm-2 and a small Tafel slope of 82 mV dec-1 in 1.0 m KOH. This bimetallic sample showed superior OER activity and stability in comparison with control materials, which could be attributed to its abundant FeNi nanoparticles, high nitrogen content, large specific surface area, and synergistic effects between Fe and Ni atoms. In addition, relevant theoretical calculation on the optimal catalyst, FeNi-NC-800, further demonstrated its efficient OER performance with effective Fe-doping in the Ni-based oxyhydroxides.

Graphene-templated growth of MoS2−Ni3S2 heterostructures as efficient electrocatalysts for overall water splitting

Due to the advantages of large specific surface area, high mass transfer efficiency and easy access to active sites, two dimensional (2D) nanomaterials provide a great opportunity for the construction of new versatile electrocatalysts with superior properties. Herein, a graphene-templated growth of MoS2-Ni3S2 heterostructure with porous structure is successfully prepared on the Ni foam (MoS2/Ni3S2@G/NF) by one pot hydrothermal method. The electronic structure and surface properties of 2D chalcogenides are modified by heterogeneous interface and component engineering, so as to prepare a high-performance transition metal composite catalytic electrode for electrochemical reaction. The optimized MoS2/Ni3S2 @G/NF shows excellent bifunctional activity and durability in alkaline medium. It only needs 53 mV and 265 mV overpotential to reach 10 mA cm−2 current density of HER and 20 mA cm−2 current density for OER, respectively. When the composite is used as an advanced electrocatalyst for water splitting, the 1.47 V voltage required to achieve a current density of 10 mA cm−2, which is better than the most non-noble metal electrocatalysts. The heterostructures between MoS2, Ni3S2 and graphene are conducive to the synchronous chemical adsorption of hydrogen and oxygen-containing intermediates, which can improve the catalytic activity of overall water splitting.