Bimetal phosphide as high efficiency and stable bifunctional electrocatalysts for hydrogen and oxygen evolution reaction in alkaline solution

The development of low-cost, high-efficiency, and stable bifunctional electrocatalysts for large-scale water electrolysis is very important for the sustainable development of energy. In this paper, the nickel cobalt phosphide (CoNiP) microstructure was prepared by the “in situ growth-ion exchange-phosphating” method. Due to the flake structure and the synergistic effect of the bimetal, the synthesized CoNiP microstructure exhibited high electrocatalytic activity and stability for hydrogen and oxygen evolution in alkaline electrolyte. The optimized CoNiP showed low overpotential of 116 mV at 10 mA cm⁻² for hydrogen evolution reaction and 400 mV at 50 mA cm⁻² for oxygen evolution reaction in KOH solution. In addition, it exhibited long-term stability at a high constant current density of 100 mA cm⁻² for 48 hours at room temperature and for 65 hours at 80 °C without significant degradation. Theoretical results showed that the introduction of Co and P atoms could reduce the reaction barrier and improve the electron transfer ability. This work provides a simple and economical way for the synthesis of electrocatalytic bimetal phosphide catalysts.

The CoNiP structure is prepared by a simple “in situ growth-ion exchange-phosphating” method. The CoNiP-0.15 M shows the excellent HER and OER performance, also it exhibits high stability with high current density at room temperature and 80 °C.     

Ru catalyst supported on nitrogen-doped nanotubes as high efficiency electrocatalysts for hydrogen evolution in alkaline media

Due to the potential application in the future energy conversion system, there is an increasing demand for efficient, stable and cheap platinum-free catalysts for hydrogen evolution. However, it is still a great challenge to develop electrocatalysts with high activity similar to platinum or even higher, especially those that can work under alkaline conditions. Ruthenium (Ru), as a cheap substitute for platinum, has been studied as a feasible substitute for (HER) catalyst for hydrogen evolution reaction. In this paper, we designed and developed a novel Ru catalyst (Ru@CNT) supported on nitrogen-doped carbon nanotubes. Electrochemical tests show that even under alkaline conditions (1 M KOH), Ru@CNT still shows excellent catalytic performance and good durability. It only needs 36.69 mV overpotential to reach a current density of 10 mA cm⁻², and its Tafel slope is 28.82 mV dec⁻¹. The catalytic performance of the catalyst is comparable to that of 20% Pt/C. The significant activity is mainly attributed to the chelation of highly dispersed ruthenium atoms on nitrogen-doped carbon nanotubes. Secondly, the one-dimensional pore structures supported by nitrogen heterocarbon nanotubes can provide more opportunities for active centers. Excellent HER performance makes Ru@CNT electrocatalyst have a broad application prospect in practical hydrogen production.

Due to the potential application in the future energy conversion system, there is an increasing demand for efficient, stable and cheap platinum-free catalysts for hydrogen evolution.     

2D TiVCTx layered nanosheets grown on nickel foam as highly efficient electrocatalysts for the hydrogen evolution reaction

Exploring highly efficient and durable catalysts for the hydrogen evolution reaction (HER) is crucial for the hydrogen economy and environmental protection issues. Numerous studies have now found that transition metal carbide MXenes are ideal candidates as catalysts for the hydrogen evolution reaction. However, MXenes are inclined to easily undergo lamellar structure agglomeration and stacking, which impedes their further applications. Besides, most of the extant research has focused on single transition metal carbides, and the investigation of double transition metal carbide MXenes is rather rare. In this research work, a three-dimensional (3D) TiVCT_x-based conductive electrode was constructed by depositing 2D TiVCT_x nanosheets on 3D network structured nickel foam (NF) to synthesize a hybrid electrode material (abbreviated as TiVCT_x@NF). TiVCT_x@NF exhibits efficient electrochemical properties with a low overpotential of 151 mV at 10 mA cm⁻² and a small Tafel slope of 116 mV dec⁻¹. Benefitting from the open layer structure and strong interfacial coupling effect, compared to the pristine structure, the resulting TiVCT_x@NF has greatly increased active sites for the hydrogen evolution reaction (HER) and encounters less resistance for charge transfer. In addition, TiVCT_x@NF exhibits better stability in long-term acidic electrolytes. This work provides a tactic to prepare three-dimensional network electrode materials and broadens the application of single transition metal carbide MXenes as water splitting electrodes in the HER, which is beneficial to the application of noble metal-free electrocatalysts.

The TiVCT_x MXene was obtained by etching and peeling methods, and the TiVCT_x@NF hybrid electrode material was obtained by the deposition method. The electrochemical performance was evaluated using a variety of characterization methods.     

Nanostructured copper molybdates as promising bifunctional electrocatalysts for overall water splitting and CO2 reduction

Overall water splitting and CO₂ reduction are two very important reactions from the environmental viewpoint. The former produces hydrogen as a clean fuel and the latter decreases the amount of CO₂ emissions and thus reduces greenhouse effects. Here, we prepare two types of copper molybdate, CuMoO₄ and Cu₃Mo₂O₉, and electrochemically investigate them for water splitting and CO₂ reduction. Our findings show that Cu₃Mo₂O₉ is a better electrocatalyst for full water splitting compared to CuMoO₄. It provides overpotentials, which are smaller than the overpotentials of CuMoO₄ by around 0.14 V at a current density of 1 mA cm⁻² and 0.10 V at −0.4 mA cm⁻², for water oxidation and hydrogen evolution reactions, respectively. However, CuMoO₄ adsorbs CO₂ and the reduced intermediates/products more strongly than Cu₃Mo₂O₉. Such different behaviors of these electrocatalysts can be attributed to their different unit cells.

Comparing overall water splitting on the surface two types of copper molybdate.     

Recent advances in the metal–organic framework-based electrocatalysts for the hydrogen evolution reaction in water splitting: a review

Water splitting is an important technology for alternative and sustainable energy storage, and a way for the production of hydrogen without generating pollution. In recent years, metal–organic frameworks (MOFs) have become the most capable multifunctional resources because of their high surface areas, tunable porosity, simple modification of compositions, and potential for use as precursors with a variety of morphological structures. Based on these qualities, many MOFs and their derived materials are utilized as electrocatalysts for the water splitting reaction. Herein, we assembled the relevant literature in recent years about MOF and MOF-derived materials for their eminent electrocatalytic activity in water splitting with useful strategies for the design and preparation of catalysts, along with challenges. This review summarizes the advancement in MOF materials, elucidating different strategies for its role in water splitting.

Water splitting is an important technology for alternative and sustainable energy storage, and a way for the production of hydrogen without generating pollution.     

First-principles study of vanadium carbides as electrocatalysts for hydrogen and oxygen evolution reactions

Vanadium carbides have attracted much attention as highly active catalysts in both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), while a satisfactory understanding of the underlying mechanisms still remains a challenge. Herein we apply first-principles calculations to systematically analyze the crystal structures, electronic properties, free energies during the HER and OER processes, surface energies and crystal formation energies of the three types of vanadium carbides, i.e., V₄C₃, V₈C₇ and VC. We show that all these vanadium carbides are metallic, which enables efficient electron transport from the bulk to the surface of the catalysts. All these vanadium carbides exhibit excellent HER performance but show poor OER catalytic activity. In particular, the V₈C₇ (110) surface shows the best catalytic performance for its relatively small |ΔG(H*)| value (−0.114 eV) for HER. Emergence of natural carbon vacancies gives rise to large surface energy, proper hydrogen adsorption energy, low crystal formation energy and weak bond strength in V₈V₇, which guarantees its leading position among the three vanadium carbides. In addition, a remarkable resemblance between VC/V₈C₇ and Pt in their electronic structures on (110) and (111) surfaces are found, which indicates a Pt-like HER mechanism in these vanadium carbides. Our results thus bring new insights to the theoretical understanding of the excellent HER performance of vanadium carbides.

The origin of excellent performance of vanadium carbides (VC and V₈V₇) in hydrogen and oxygen evolution reactions (HER and OER) is revealed by first-principles calculations. It is found that the underlying mechanisms in HER/OER processes are Pt-like.     

Boosting the hydrogen evolution reaction activity of Ru in alkaline and neutral media by accelerating water dissociation

Electrochemical water splitting via a cathodic hydrogen evolution reaction (HER) is an advanced technology for clean H₂ generation. Ru nanoparticle is a promising candidate for the state-of-the-art Pt catalyst; however, they still lack the competitiveness of Pt in alkaline and neutral media. Herein, a ternary HER electrocatalyst involving nano Ru and Cr₂O₃ as well as N-doped graphene (NG) that can work in alkaline and neutral media is proposed. Cr₂O₃ and NG feature strong binding energies for hydroxyl and hydrogen, respectively, which can accelerate the dissociation of water, whereas Ru has weak hydrogen binding energy to stimulate hydrogen coupling. The HER activity of Ru is greatly enhanced by the promoted water-dissociation effect of NG and Cr₂O₃. To achieve a current density of 10 mA cm⁻², the as-obtained Ru–Cr₂O₃/NG only needs a very low overpotential of 47 mV, which outperforms the activity of Pt/C in alkaline media. The strategy proposed here, multi-site acceleration of water dissociation, provides new guidance on the design of a highly efficient, inexpensive, and biocompatible HER catalyst in nonacidic condition.

The electrocatalytic activity of Ru in non-acidic media for hydrogen evolution reaction can be greatly boosted by Cr₂O₃ and N-doped graphene.     

N-doped mixed Co,Ni-oxides with petal structure as effective catalysts for hydrogen and oxygen evolution by water splitting

Developing electrocatalytic nanomaterials for green H₂ energy is inseparable from the exploration of novel materials and internal mechanisms for catalytic enhancement. In this work, nano-petal N-doped bi-metal (Ni, Co) and bi-valence (+2, +3) (Ni_1−xCo_x)²⁺Co₂³⁺O₄ compounds have been in situ grown on the surface of Ni foam. The N³⁻ atoms originate from the amino group in urea and doped in the compound during annealing. The as-synthesized N-doped (Ni_1−xCo_x)²⁺Co₂³⁺O₄ nano-petals demonstrate commendable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) bi-functional catalytic efficiency and stability. Electrochemical measurements confirm that the nitrogen doping significantly improves the catalytic kinetics and the surface area. Density functional theory calculations reveal that the improved HER and OER kinetics is not only due to the synergistic effect of bi-metal and bi-valence, as well as the introduction of defects such as oxygen vacancies, but also it more depends on the shortened bond length between the nitrogen N³⁻ atoms and the metal atoms, and the increased electron density of the metal atoms attached to the N³⁻ atoms. In other words, the change of lattice parameters caused by nitrogen doping is more conducive to the catalytic enhancement than the synergistic effect brought by bi-metal. This study provides an experimental and theoretical reference for the design of bi-functional electrocatalytic nanomaterials.

Developing electrocatalytic nanomaterials for green H₂ energy is inseparable from the exploration of novel materials and internal mechanisms for catalytic enhancement.     

MOF derived carbon based nanocomposite materials as efficient electrocatalysts for oxygen reduction and oxygen and hydrogen evolution reactions

The escalating global energy demands and the formidable risks posed by fossil fuels coupled with their rapid depletion have inspired researchers to embark on a quest for sustainable clean energy. Electrochemistry based technologies, e.g., fuel cells, Zn–air batteries or water splitting, are some of the frontrunners of this green energy revolution. The primary concern of such sustainable energy technologies is the efficient conversion and storage of clean energy. Most of these technologies are based on half-cell reactions like oxygen reduction, oxygen and hydrogen evolution reactions, which in turn depend on noble metal based catalysts for their efficient functioning. In order to make such green energy technologies economically viable, the need of the hour is to develop new noble metal free catalysts. Porous carbon, with some assistance from heteroatoms like N or S or earth abundant transition metal or metal oxide nanoparticles, has shown excellent potential in the catalysis of such electrochemical reactions. Metal–organic frameworks (MOFs) containing metal nodes and organic linkers in an ordered morphology with inherent porosity are ideal self-sacrificial templates for such carbon materials. There has been a recent spurt in reports on such MOF-derived carbon based materials as electrocatalysts. In this review, we have presented some of this research work and also discussed the practical reasons behind choosing MOFs for this purpose. Different approaches for synthesizing such carbonaceous materials with unique morphologies and doping, targeted towards superior electrochemical activity, have been documented in this review.

Hetero-atom doped porous carbon materials derived from MOFs are efficient noble metal-free electrocatalysts.     

Sponge-like N-doped carbon materials with Co-based nanoparticles derived from biomass as highly efficient electrocatalysts for the oxygen reduction reaction in alkaline media

The development of highly efficient and low-cost catalysts towards Oxygen Reduction Reaction (ORR) is of significance for renewable energy technologies such as proton-exchange membrane fuel cells and metal–air batteries. This study is to utilize the biomass of soybean straw as the supporting carbon materials to prepare nitrogen and cobalt dual-doped porous biocarbon electrocatalysts (CoNASS) possessing high content of N (1.92%), embedding cobalt nanoparticles and sponge-like structure with high specific surface area (1185.00 m² g⁻¹) as well as appropriate pore diameter (∼2.17 nm). Meantime, CoNASS exhibits a good electrocatalytic activity with a half-wave potential of 0.786 V (vs. RHE), comparable to a half-wave potential of 0.827 V (vs. RHE) for the commercial Pt/C. The detections of electrochemical kinetics show the electron transfer number of CoNASS is in the range of 3.84–3.92, which indicates 4-electron pathway dominantly occurs in ORR. And the limiting diffusion current density of CoNASS at 1600 rpm is around 5.8 mA cm⁻² slightly higher than that of the benchmark Pt/C (5.6 mA cm⁻²). This work opens a new avenue to utilize soybean straw, one of agriculture waste of large quantity, to prepare high efficient and low-cost catalysts for ORR.

Sponge-like N-doped carbon materials with Co-based nanoparticles derived from biomass as high efficient electrocatalysts for oxygen reduction reaction.     

Advantage of semi-ionic bonding in fluorine-doped carbon materials for the oxygen evolution reaction in alkaline media

Metal-free carbonaceous catalysts have potential applications for oxygen evolution reaction (OER) devices because of their low-cost and abundant supply. We report that fluorine-doped carbon black is an active catalyst for OER. Fluorine-doped carbon black (F-KB) is simply synthesized by the pyrolysis of KETJENBLACK (KB) as carbon substrate with Nafion as fluorine precursor. As a result, the OER activity of F-KB is significantly higher than that of pristine KB in alkaline media. The OER catalytic activity of F-KB is found to be dependent on the quantity and characteristics of carbon-fluorine bonding (C–F) which can be controlled by the pyrolysis temperature. It is further found that the OER activity depends on the quantity of semi-ionic C–F bonds, but not covalent C–F bonds. This result proves the importance of carbon atoms with semi-ionic C–F bonds as the active sites for OER.

Fluorine-doped carbon has a higher electrocatalytic oxygen evolution activity than pristine carbon black in alkaline media. The activity of oxygen evolution and characteristics of carbon to fluorine bond are controlled by pyrolysis temperature of Nafion.     

Novel heterostructure Cu2S/Ni3S2 coral-like nanoarrays on Ni foam to enhance hydrogen evolution reaction in alkaline media

Exploring efficient alternatives to precious noble metal catalysts is a challenge. Here, a new type of non-noble metal Cu₂S/Ni₃S₂ heterostructure nanosheet array is fabricated on 3D Ni foam. This electrocatalyst has excellent activity and durability to Hydrogen Evolution Reaction (HER) under alkaline conditions. The synergistic catalysis produced by the {$\bar{2}$10} and (034) crystal planes and the increase in charge transfer and the number of active sites caused by lattice defects greatly improve the electrocatalytic activity of Ni₃S₂. In the HER process, the Cu₂S/Ni₃S₂ interface increases the formation of S–H bonds, and Cu₂S promotes the transformation during the HER process into S-doped CuO, optimizing the adsorption capacity of S-doped sites for H. Among electrocatalysts made with different feed ratios, Cu₂S/Ni₃S₂/NF-3, for HER, only needs an overpotential of 50 mV to deliver a current density of 10 mA cm⁻². This work provides a promising non-noble metal electrocatalyst for water splitting under alkaline conditions.

We fabricated a heterostructure Cu₂S/Ni₃S₂ nanosheet array, which can accelerate charge transfer and provide more active sites. This work provides a promising non-noble metal electrocatalyst for water splitting under alkaline conditions.     

Precursor accumulation on nanocarbons for the synthesis of LaCoO3 nanoparticles as electrocatalysts for oxygen evolution reaction

Oxygen evolution reaction (OER) is a key step in energy storage devices. Lanthanum cobaltite (LaCoO₃) perovskite is an active catalyst for OER in alkaline solutions, and it is expected to be a low-cost alternative to the state-of-the-art catalysts (IrO₂ and RuO₂) because transition metals are abundant and inexpensive. For efficient catalysis with LaCoO₃, nanosized LaCoO₃ with a high surface area is desirable for increasing the number of catalytically active sites. In this study, we developed a novel synthetic route for LaCoO₃ nanoparticles by accumulating the precursor molecules over nanocarbons. This precursor accumulation (PA) method for LaCoO₃ nanoparticle synthesis is simple and involves the following steps: (1) a commercially available carbon powder is soaked in a solution of the nitrate salts of lanthanum and cobalt and (2) the sample is dried and calcined in air. The LaCoO₃ nanoparticles prepared by the PA method have a high specific surface area (12 m² g⁻¹), comparable to that of conventional LaCoO₃ nanoparticles. The morphology of the LaCoO₃ nanoparticles is affected by the nanocarbon type, and LaCoO₃ nanoparticles with diameters of less than 100 nm were obtained when carbon black (Ketjen black) was used as the support. Further, the sulfur impurities in nanocarbons significantly influence the formation of the perovskite structure. The prepared LaCoO₃ nanoparticles show excellent OER activity owing to their high surface area and perovskite structure. The Tafel slope of these LaCoO₃ nanoparticles is as low as that of the previously reported active LaCoO₃ catalyst. The results strongly suggest that the PA method provides nanosized LaCoO₃ without requiring the precise control of chemical reactions, harsh conditions, and/or special apparatus, indicating that it is promising for producing active OER catalysts at a large scale.

A simple synthetic process for LaCoO₃ nanoparticles based on the accumulation of precursors on nanocarbon supports was presented. The LaCoO₃ nanoparticles showed excellent OER activity owing to their high surface area and perovskite structure.     

Hierarchical Ni–Co–O–C–P hollow tetragonal microtubes grown on Ni foam for efficient overall water splitting in alkaline media

Exploring low-cost and highly efficient non-noble bifunctional electrocatalysts with high performances for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential for large-scale sustainable energy systems. Herein, the Ni–Co–O–C–P hollow tetragonal microtubes grown on 3D Ni foam (Ni–Co–O–C–P/NF) was synthesized via a one-step solvothermal method and followed by a simple carbon coating and in situ phosphorization treatment. Benefiting from the unique open and hierarchical nano-architectures, the as prepared Ni–Co–O–C–P/NF presents a high activity and durability for both the HER and OER in alkaline media. The overall-water-splitting reaction requires a low cell voltage (1.54 V @ 10 mA cm⁻²) in 1 M KOH when Ni–Co–O–C–P/NF is used as both the anode and cathode. The highly flexible structure can provide a large amount of exposed active sites and shorten the mass transport distance. Furthermore, bimetallic phosphides also favor the electrocatalysis due to the higher electronic conductivity and the synergetic effect. This work demonstrated a promising bifunctional electrocatalyst for water electrolysis in alkaline media with potential in future applications.

Herein, the Ni–Co–O–C–P hollow tetragonal microtubes grown on 3D Ni foam (Ni–Co–O–C–P/NF) was delicately designed and synthesized, which presented a high activity and durability for electrocatalytic overall-water-splitting in alkaline media.     

One-step chemical vapor deposition fabrication of Ni@NiO@graphite nanoparticles for the oxygen evolution reaction of water splitting

NiO combined with conductive materials is a practicable way to improve its catalytic property for the oxygen evolution reaction (OER) by enhancing its electrical conductivity. Herein, Ni@NiO@graphite nanoparticles less than 20 nm in average diameter were synthesized by a one-step chemical vapor deposition process. Due to the deliberately controlled lack of oxygen, Ni particles and carbon clusters decomposed from NiCp₂ precursors were oxidized incompletely and formed Ni@NiO core–shell nanoparticles coated by a graphite layer. The thickness of the graphite layer and the content of Ni were controlled by varying deposition temperature. The electrochemical activity towards the oxygen evolution reaction was assessed within alkaline media. Compared with commercial NiO powder, the Ni@NiO@graphite nanoparticles with the unique core–shell microstructure exhibit excellent OER performance, i.e., an overpotential of 330 mV (vs. RHE) at 10 mA cm⁻² and a Tafel slope of 49 mV dec⁻¹, due to the improved electrical conductivity and more active sites. This work provides a facile and rapid strategy to produce nanoparticles with unique microstructures as highly active electrocatalysts for the OER.

Ni@NiO@graphite nanoparticles with excellent OER performance were synthesized by a one-step chemical vapor deposition process.     

Ultradispersed IrxNi clusters as bifunctional electrocatalysts for high-efficiency water splitting in acid electrolytes

Design and synthesis of electrocatalysts with high activity and low cost is an important challenge for water splitting. We report a rapid and facile synthetic route to obtain Ir_xNi clusters via polyol reduction. The Ir_xNi clusters show excellent activity for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acidic electrolytes. The optimized Ir₂Ni/C clusters exhibit an electrochemical active area of 18.27 mF cm⁻², with the overpotential of OER being 292 mV and HER being 30 mV at 10 mA cm⁻², respectively. In addition, the Ir₂Ni/C used as the cathode and anode for the H-type hydrolysis tank only needs 1.597 V cell voltages. The excellent electrocatalytic performance is mainly attributed to the synergistic effect between the metals and the ultra-fine particle size. This study provides a novel strategy that has a broad application for water splitting.

A method of preparing Ir_xNi/C clusters by polyol reduction using a XC-72R support was proposed. Due to the 2 nm size of the catalyst particles, more active sites are exposed. This is a promising route for the development of efficient water splitting electrocatalysts.     

Three-dimensional reduced graphene oxide decorated with cobalt metaphosphate as high cost-efficiency electrocatalysts for the hydrogen evolution reaction

The development of cost-effective non-noble metal electrocatalysts is critical for the research of renewable energy. Transition metal cobalt metaphosphate-based materials have the potential to replace the noble metal Pt. Hence, in this work, we synthesize three-dimensional graphene-supported cobalt metaphosphate (Co(PO₃)₂-3D RGO) for the first time through the one-step hydrothermal synthesis method at low temperature with the aid of PH₃ phosphating. In a 0.5 mol L⁻¹ H₂SO₄ solution, the obtained electrocatalyst exhibits excellent electrochemical activity for the hydrogen evolution reaction (HER) with a small overpotential of 176 mV at a current density of 10 mA cm⁻² and a Tafel slope of 63 mV dec⁻¹. Additionally, in a 1 mol L⁻¹ KOH solution, the electrocatalyst also shows outstanding HER activity with a small overpotential of 158 mV at a current density of 10 mA cm⁻² and a Tafel slope of 88 mV dec⁻¹. Co(PO₃)₂-3D RGO can maintain its catalytic activity for at least ten hours whether in acid or alkali. This work not only demonstrates an excellent electrocatalyst for the hydrogen evolution reaction, but also provides an extremely convenient preparation technology, which provides a new strategy for the development and utilization of high-performance electrocatalysts.

The development of cost-effective non-noble metal electrocatalysts is critical for the research of renewable energy.     

An advanced and efficient Co3O4/C nanocomposite for the oxygen evolution reaction in alkaline media

The design of efficient nonprecious catalysts for the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER) is a necessary, but very challenging task to uplift the water-based economy. In this study, we developed a facile approach to produce porous carbon from the dehydration of sucrose and use it for the preparation of nanocomposites with cobalt oxide (Co₃O₄). The nanocomposites were studied by the powder X-ray diffraction and scanning electron microscopy techniques, and they exhibited the cubic phase of cobalt oxide and porous structure of carbon. The nanocomposites showed significant OER activity in alkaline media, and the current densities of 10 and 20 mA cm⁻² could be obtained at 1.49 and 1.51 V versus reversible hydrogen electrode (RHE), respectively. The impedance study confirms favorable OER activity on the surface of the prepared nanocomposites. The nanocomposite is cost-effective and can be capitalized in various energy storage technologies.

The design of efficient nonprecious catalysts for the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER) is a necessary, but very challenging task to uplift the water-based economy.     

Ni foam electrode solution impregnated with Ni-FeX(OH)Y catalysts for efficient oxygen evolution reaction in alkaline electrolyzers

Oxygen evolution reaction (OER) is a demanding step within the water splitting process for its requirement of a high overpotential. Thus, to overcome this unfavourable kinetics, an efficient catalyst is required to expedite the process. In this context, we report on Ni foam functionalised with low cost iron (Fe) and iron hydroxide (Fe(OH)_X), wet chemically synthesized as OER catalysts. The prepared catalyst based on iron hydroxide precipitate shows a promising performance, exhibiting an overpotential of 270 mV (at a current density of 10 mA cm⁻² in 1 M KOH solution), an efficient Tafel slope of ∼50 mV dec⁻¹ and stable chronopotentiometry. The promising performance of the anode was further reproduced in the overall water splitting reaction with a two electrode cell. The overall reaction requires a lower potential of 1.508 V to afford 10 mA cm⁻², corresponding to 81.5% electrical to fuel efficiency.

Modification of Ni foam electrode by FeCl₃·6H₂O and HCl, towards superior oxygen-evolving electrocatalyst for water splitting process.     

Au@PdAg core–shell nanotubes as advanced electrocatalysts for methanol electrooxidation in alkaline media

Developing active and cost-effective electrocatalysts for methanol electrooxidation is crucial to the commercialization of direct methanol fuel cells (DMFCs). In this study, Au@PdAg core–shell nanotubes are synthesized in an aqueous solution by sequential galvanic displacement between Ag nanowires and AuCl₄⁻ and PdCl₄²⁻. High-resolution transmission electron microscopy studies demonstrate that the obtained Au@PdAg nanotubes consist of a Au-rich interior that is encapsulated with a three-dimensionally dendritic, porous PdAg alloy shell, forming a core–sheath nanostructure. Electrochemical studies indicate that the as-prepared Au@PdAg nanotubes exhibit apparent electrocatalytic activity and stability towards methanol electrooxidation in alkaline media. This remarkable high performance can be attributed to their large specific surface area and unique porous morphology.

Au@PdAg core–shell nanotubes using the galvanic displacement reaction were prepared and they exhibited excellent electrocatalytic performance towards methanol electrooxidation.