Bifunctional Electrocatalysts Research Articles

Self-supported nanoflower-like CoNiSe2/NF as an efficient bifunctional electrocatalyst

Self-supported nanoflower-like CoNiSe2/NF as an efficient bifunctional electrocatalyst

Development of a free-standing flexible electrode for efficient overall water-splitting performance via electroless deposition of iron-nickel-cobalt on polyacrylonitrile-based carbon cloth

Developing cost-effective and highly efficient electrodes for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is crucial, particularly for alkaline OER and HER. Herein, electroless plating of iron-nickel–cobalt (Fe–Ni–Co) electrocatalyst on a flexible polyacrylonitrile (PAN)-based carbon cloth (CC) was performed to synthesize a free-standing catalytic electrode for bifunctional electrocatalysts. The three-dimensional porous backbone of PAN-based CC and the synergistic effect between Fe-Ni-Co and corresponding hydroxides result in outstanding OER and HER activities, that is low overpotentials of 230 and 150 mV at 10 mA cm−2 and Tafel slopes of 63 and 57.1 mV dec–1, respectively. Additionally, a complete alkaline electrolyzer was constructed using Fe-Ni-Co plated PAN-based CC as both the cathode and anode. When operated at 10 mA cm−2, this setup enabled efficient water splitting at a low potential of 1.57 V. This study provides new opportunities for the development of advanced Fe-Ni-Co electrocatalyst with superior bifunctional OER and HER performance and cost-effectiveness that are suitable for integration into PAN-based CC via electroless plating.

Highly efficient oxygen carrier NiFeP (oxy) hydroxides nanoparticle embedded in N-doped porous carbon derived from bio-waste for bifunctional electrocatalysts

Developing cost-effective, readily available materials for efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting is a crucial step toward enhancing the profitability and sustainability of energy conversion systems. This research introduces a novel synthesis method for NiFeP/NPC OHs from banana peel bio-waste, a method that could revolutionize the field of materials science and electrochemistry. The use of metallic phosphides, known for their excellent electrical conductivity and catalytic activity, as bifunctional catalysts, combined with the efficient synthesis of nanoporous carbons (NPC) from banana peel bio-waste (BPW), could pave the way for a new era of sustainable and cost-effective energy conversion. By chemically activating different porogens, such as nickel, iron, and phosphorus (NiFeP), to form (oxy) hydroxides (OHs), functional carbonaceous structures with a high density of pores and large specific surface areas can be achieved. The resulting materials, designated as NiFeP/NPC OHs, are characterized by their remarkable porosity, high conductivity, large surface area, and chemical stability. These properties make NiFeP/NPC OHs particularly suitable for electrocatalysis, where they exhibit outstanding activity in both HER and OER. The optimized NiFeP/NPC OHs material shows a very low overpotential of 93 mV for HER and 243 mV for OER at 10 mA cm⁻2 and high durability over 100 h. Moreover, the bifunctional NiFeP/NPC OHs electrode demonstrates exceptional catalytic activity and stability in alkaline solutions. This study not only highlights the innovative synthesis of NPC from BPW and the cost-effective fabrication of NiFeP/NPC OHs but also sparks curiosity about the potential of this novel synthesis method.

First principles study of V2CT2-based MXenes materials in oxygen reduction and oxygen evolution reactions

The development of bifunctional ORR/OER electrocatalysts with low cost, high activity and sustainable cycle plays an important role in improving the performance of new green energy storage and conversion devices to alleviate the energy crisis and environmental pollution. As a graphene-like two-dimensional inorganic layered compound with unique electrochemistry, MXenes materials have attracted more and more attention in the field of electrocatalytic applications. In this paper, based on the first-principles calculation method based on density functional theory (DFT) and quantum mechanics, an effective scheme for designing efficient ORR/OER bifunctional electrocatalysts by introducing Pd/Pt single atoms to regulate the electronic structure of V2CT2 (T = O, F) is proposed. Firstly, we discussed the stability of the designed series of single-atom catalysts by calculating the formation energy, binding energy and molecular dynamics simulation. Secondly, by comparing the theoretical overpotentials of these single-atom catalysts for ORR and OER, we found that among the designed SACs, V2CO2-Pd, V2CF2-Pd and V2CO2-VO-Pt are catalysts with good bifunctional catalytic activity for ORR/OER. Our work provides some guidance for the application of MXenes materials in the field of electrocatalysis.

Reinforced interfacial coupling effect of NiO/Ni2P by Fe doping for boosting water splitting

Nickel-based catalysts are suitable for water splitting to generate hydrogen. However, the low conductivity and weak stability have always been urgent issues to be addressed in nickel-based catalysts. Fe-doped nickel oxide/nickel phosphide (Fe-NiO/Ni2P) was prepared as a bifunctional electrocatalyst by doping metal and constructing heterogeneous interface. The introduction of Fe contributed to the reinforced interfacial coupling effect of NiO/Ni2P to promote charge transfer and accelerate reaction kinetics. The heterojunction regulated the interfacial charge density between NiO and Ni2P to improve the electronic environment of Ni2+ and enhance conductivity. The O-Fe-P bond at the heterogeneous interface induced the directional transfer of electrons and ensured the structure stability. The synergistic effect of Fe doping and heterogeneous interface increased the adsorption energy of *O and coordinated the adsorption energy of *H, advancing the catalytic performance. Fe-NiO/Ni2P exhibited the overpotential of 242 mV and 141 mV at 10 mA cm−2 for oxygen and hydrogen evolution, respectively.

Axial modulation of catalysis mechanism via charge-asymmetric for enhanced electrocatalytic performance toward hydrogen and oxygen evolution reactions

Designing efficient, stable, and nonprecious metal bifunctional catalysts is warranted for realizing the industrial application of electrocatalytic overall water splitting. Herein, we report a new catalyst (CoFe/SNC) for the HER and OER. The active site of catalysis composed of two charge-asymmetric Co/Fe atoms could axial modulation of the catalysis mechanism, thus improving the kinetics of the HER and OER. Moreover, the use of hollow porous carbon spheres as catalyst support not only enhances the distribution of Co/Fe atoms but also improves the mass transfer during the HER and OER processes. Therefore, the CoFe/SNC displays a good alkaline HER and OER activity with a small overpotential of 96.2 mV and 285.8 mV at 10 mA cm−2, respectively. Theoretical calculations reveal that the Fe atoms with optimal absorption energy for the hydrogen intermediate and the Co centers with a reduced energy barrier for the rate-determining step are the active sites for HER and OER, respectively. Additionally, the synergistic effect of Co/Fe dual-atoms could effectively optimize the intermediate adsorption of Co/Fe-N4 sites and improve the barriers of HER and OER activity and stability. This study provides valuable insight for designing bifunctional alkaline water-splitting electrocatalysts.

Adaptive Active Site Turning for Superior OER and UOR on Ir‐Ni3N Catalyst

AbstractRenewable energy‐based electrocatalytic oxidation for hydrogen production in complex reaction environments such as industrial wastewater and human urine demands high‐performing catalysts to conduct switchable urea oxidation reactions (UOR) and traditional oxygen evolution reactions (OER). Here, a novel bifunctional nanosheet electrocatalyst is reported, Ir‐Ni3N, which exhibits excellent electrocatalytic activity for both OER and UOR under alkaline conditions. Specifically, the overpotentials at 100 mA cm−2 for OER and UOR are 1.59 and 1.37 V vs. reversible hydrogen electrode (RHE) respectively, which are superior to most of the recently reported nickel‐based catalysts. Accordingly, a comprehensive mechanism for competitive catalytic activities of Ni and Ir sites in Ir‐Ni3N and the switch between OER and UOR that guarantees consistent hydrogen production is proposed. This study provides a feasible strategy for continuous hydrogen production aided by reagent‐adaptive electrocatalysts in urea‐containing wastewater.

Bifunctional heterostructured nitrogen-doped carbon-layer-loaded NiSe2-FeSe2 electrocatalyst for efficient water splitting

Developing high-performance, eco-friendly bifunctional electrocatalysts is crucial to popularizing water electrolysis for hydrogen production, but it still presents major challenges. Here, we develop a composite material with NiSe2-FeSe2 heterostructure loaded on N-doped carbon layers by utilizing the metal-organic framework as a sacrificial template (NiSe2-FeSe2/NC). According to microstructural studies, direct contact between NiSe2 and FeSe2 induces charge transfer and enhances conductivity, while sensible arraying of NiSe2-FeSe2/NC nanosheets fully exposes active sites and protects catalysts from violent reaction processes. The NiSe2-FeSe2/NC heterostructured catalysts show excellent bifunctional catalytic activity for hydrogen and oxygen evolution reactions, with overpotentials of 54 and 232 mV at 10 mA cm−2, respectively. Moreover, NiSe2-FeSe2/NC also retains superiority in a two-electrode system, needing lower voltage to drive the overall water splitting at 10 mA cm−2 (1.53 V) than Pt/C||RuO2 as well as long-term stability. This work introduces a novel concept for developing state-of-the-art non-noble metal catalysts for hydrogen production and new insights into interface engineering.

Bimetal Metaphosphate/Molybdenum Oxide Heterostructure Nanowires for Boosting Overall Freshwater/Seawater Splitting at High Current Densities.

Exploring excellent non-noble bifunctional electrocatalysts for freshwater/seawater splitting at high current densities has attracted extensive interest owing to strong anodic oxidation and severe chloride corrosion challenges. Herein, hierarchical bimetal Ni-Co metaphosphate/molybdenum oxide heterostructure nanowires (NiCoMoPO) are rationally designed and fabricated to efficiently boost oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline freshwater/seawater, where the favorable electronic structure from heterostructures, signified by X-ray absorption spectra, endows NiCoMoPO with the enhanced intrinsic activity, while its hierarchical nanowire structure and heterostructures provide abundant active sites. Additionally, the PO3 - improves the chloride-corrosion resistance and efficiently facilitates the OER kinetics verified by theoretical and experimental studies. Therefore, NiCoMoPO drives 1000mA cm-2 at low overpotentials of 467 and 442mV for OER and HER in alkaline freshwater respectively, as well as a small cell voltage of 2.135V for overall freshwater splitting with robust durability of 300h. Impressively, due to the strong corrosion resistance, at 500mA cm-2 of overall seawater splitting, NiCoMoPO maintains almost 2.096V for 1200h, indicating promising practical applications. This work sheds light on the rational design and fabrication of outstanding electrocatalysts at high current densities of seawater/freshwater splitting.

NiP/Fe3P/MoP@NF nanoblocks as a bifunctional electrocatalyst for water splitting in alkaline seawater and urea solution

Compared with conventional electrolytic fresh water for hydrogen generation, electrolytic seawater for hydrogen production is more cost-effective, because seawater resources are rich, and fresh water resources are short. However, there are many impurity ions in seawater, especially chloride ions, which have great corrosion on the catalyst, so it is a major factor restricting the development of electrolytic seawater. In this study, a novel NiP/Fe3P/MoP@NF catalyst was made via conventional hydrothermal and phosphating method. Experimental results show that the overpotential of NiP/Fe3P/MoP@NF catalyst in the current density of 10 mA cm−2 is just 40 mV for hydrogen evolution reaction (HER) and the overpotential of NiP/Fe3P/MoP@NF catalyst in the same condition is 135 mV for oxygen evolution reaction (OER) in 1 M KOH and seawater solution. In electrolyte solution of 0.5 M urea and 1 M KOH, the overpotential of NiP/Fe3P/MoP@NF catalyst in the same current density of 10 mA cm−2 is 51 mV for HER. Furthermore, the whole alkaline seawater splitting requires an applied voltage of 1.66 V at current density of 10 mA cm−2. Experimental results show that the increased catalytic activity is assigned to the rapid electron transport rate, the exposure of more activity sites, and their synergistic catalysis. The density functional theory (DFT) can show that MoP has the best Gibbs free energy for hydrogen and electrical conductivity compared with NiP and Fe3P, thus enhancing the catalytic performance of NiP/Fe3P/MoP@NF. The paper proposes novel ideas concerning the exploration of catalysts in alkaline seawater and urea solution.

Enhanced Oxygen‐Reaction Electrocatalysis and Corrosion Resistance of CoCrFeNi Thin Films by Tuned Microstructure and Surface Oxidation

Oxygen electrocatalysts play a key role in renewable and fossil‐free energy production. Bifunctional catalysts active for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) allow use of the same material system for both energy production (ORR) and fuel generation (OER). However, optimizing the performance of bifunctional catalysts requires in depth understanding of the catalyst structure, its surface chemistry in terms of active sites and the underlying catalytic mechanism. Here, the catalytic performance of CoCrFeNi thin films is investigated, synthesized using high‐power impulse magnetron sputtering, as bifunctional oxygen electrocatalysts. The film crystal structure and morphology, and thereby the catalytic performance, can be tuned by the ion acceleration (bias) to the substrate. To further enhance the catalytic activity, anodization is used to electrochemically modify the films, forming a thicker oxide layer enriched in Co and Ni cations which significantly improves the ORR performance. Anodization improves the catalyst stability during OER, with an OER potential of 1.45 V versus the reversible hydrogen electrode (RHE) at 10 mA cm−2 for more than 24 h. While the corrosion resistance is high both before and after anodization, in terms of catalytic activity the anodized films outperformed the as‐deposited ones. This makes anodized films excellent electrocatalyst candidates in corrosive alkaline environments such as fuel cells and electrolyzers.

Simultaneous efficient production of hydrogen peroxide, urea and H2 by bifunctional Cu-doped TiO2 electrocatalyst from CO2, N2 and water

The production of three separated, high-value chemicals (H2O2, urea and H2) from CO2, N2, and H2O represents a significant challenge. It is a prospective and innovative way to simultaneously produce these chemicals in an anion exchange membrane (AEM) electrolyzer, which couples anodic 2e- water oxidation (2e-WOR) and cathodic CO2, N2 and water reduction reaction (CNWRR), but has not yet been realized. Here, we found that bifunctional CuxTi1-xO2-y catalysts can be employed in the electrochemical production of H2O2, urea and H2 from CO2, N2 and water, and the optimized Cu0.12Ti0.88O2-y catalyst exhibits an excellent productivity of 11.8 μmol cm−2 min−1, 0.3 mg cm-2h−1 and 0.82 mmol cm-2h−1 for H2O2, urea and H2 at 4.0 V (50 mA cm−2) in AEM electrolyzer, respectively. Theoretical calculations reveal that the superior performance of the 2e-WOR and CNWRR is attributed to the Cu doping effect, which not only promotes the coupling of *OH but also optimizes the adsorption energy barriers of COOH* and NNH*. It is worth noting that the AEM electrolyzer assembled by bifunctional Cu0.12Ti0.88O2-y reaches a current density of 50 mA cm−2 with a cell voltage of 4.0 V and exhibits excellent stability of 50-hour continuous operation.

Nickel-copper alloying arrays realizing efficient co-electrosynthesis of adipic acid and hydrogen

Constructing electrocatalytic overall reaction technology to couple the electrosynthesis of adipic acid with energy-saving hydrogen production is of significant for sustainable energy systems. However, the development of highly-active bifunctional electrocatalysts remains a challenge. Herein, 3D hierarchical nickel-copper alloying arrays with dendritic morphology are manufactured by a simple electrodeposition process, standing for the excellent bifunctional electrocatalyst towards the co-production of adipic acid and H2 from cyclohexanone and water. The membrane-free flow electrolyzer of Cu0.81Ni0.19/NF shows the superior electrooxidation performance of ketone-alcohol (KA) oil with high faradaic efficiencies of over 90% for adipic acid and H2, robust stability over 200 h as well as a high yield of 0.6 mmol h−1 for adipic acid at 100 mA cm−2. In-situ spectroscopy indicates the Cu0.81Ni0.19 alloy contributes to forming more active NiOOH species to involve in the conversion of cyclohexanone to adipic acid, while the proposed reaction pathway undergoes the 2-hydroxycyclohexanone and 2,7-oxepanedione intermediates. Moreover, the theoretical calculations confirm that the optimal electronic interaction, boosted reaction kinetics as well as improved adsorption free energy of reaction intermediates, synergistically endows Cu0.81Ni0.19 alloy with superior bifunctional performance.

Partial oxidation of Rh/Ru nanoparticles within carbon nanofibers for high-efficiency hydrazine oxidation-assisted hydrogen generation

Hydrazine oxidation reaction (HzOR), an alternative to oxygen evolution reaction, effectively mitigates hydrazine pollution while achieving energy-efficient hydrogen production. Herein, partially oxidized Ru/Rh nanoparticles embedded in carbon nanofibers (CNFs) are fabricated as a bifunctional electrocatalyst for hydrogen evolution reaction (HER) and HzOR. The presence of multiple components including metallic Ru and Rh and their oxides provides numerous electrochemically active sites and superior charge transfer properties, thus improving the electrocatalytic performance. Additionally, the confinement of the active components within CNFs further enhances structural stability. Consequently, the optimized electrocatalyst exhibits ultralow overpotentials of 16 mV at 10 mA cm−2 and 176 mV to reach an industry-level current density of 1 A cm−2 for HER, considerably outperforming the benchmark Pt/C catalyst. Furthermore, it shows an outstanding anodic HzOR activity, achieving a small potential of –0.019 V to generate 10 mAcm−2. A two-electrode overall hydrazine splitting (OHzS) cell prepared using the electrocatalyst operates at a compelling voltage that is 1.953 V lower than that of the overall water splitting (OWS) cell at 200 mA cm−2. Furthermore, the OHzS cell achieves a hydrogen production rate of 1.17 mmol h−1, which is 15-fold that of OWS. Additionally, Rh1Ru1Ox-CNFs-350 is used to construct a Zn-hydrazine battery with excellent performance. This study presents an effective system for achieving high-yielding green H2 production with low energy consumption while simultaneously addressing hydrazine pollution.

Copper-doped zinc cobalt sulfide nanosheets as advanced bifunctional electrocatalysts for sustainable hydrogen production via electrochemical water splitting

Copper-doped zinc cobalt sulfide nanosheets as advanced bifunctional electrocatalysts for sustainable hydrogen production via electrochemical water splitting

Carbon cloth-based meteorite-like Co–CuS/MoS2 heterostructure for efficient water electrolysis

Developing low-cost, high-efficiency electrocatalysts is critically important for efficient hydrogen production. In this study, a novel electrocatalyst, Co–CuS/MoS2 nanocomposite, was successfully synthesized via ion exchange on carbon cloth using Evans-Showell type polyoxometalate (NH4)6 [Co2Mo10O38H4]·11H2O (Co2Mo10) as a precursor and thiourea in a hydrothermal reaction. The optimized Co–CuS/MoS2 exhibited outstanding hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities, with overpotentials of 90 mV and 270 mV at a current density of 10 mA cm−2, respectively, and demonstrated long-term stability in alkaline electrolytes. The superior performance of this catalyst is attributed to the high charge transfer rates between MoS2 and CuS, abundant heterostructure interfaces, and efficient diffusion channels. This study provides a new design strategy for exploring efficient bifunctional electrocatalysts.

Metal organic framework derived N, P co-doped carbon coated Mo2C-Co6Mo6C hetero-structural nano bowl for efficiency overall water splitting

It is still important and challenge to explore bifunctional electrocatalysts with high catalytic activity for overall water splitting. Constructing heterostructure catalysts can integrate catalytic active species with different function as well as modify the catalytic activity of single component. In this work, by rational designing ZnCoMo metal organic framework (MOF) as the precursor, we successfully prepare Mo2C-Co6Mo6C nano bowl and investigate its potential for full water splitting. Due to the co-existence of highly active catalytic species of Mo2C and Co6Mo6C, the large specific surface area induced by the evaporation of Zn during calcination process, and the nano bowl-like morphology that boosts mass transfer, the as prepared ZnCoMo-900 can catalyze both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) effectively. Especially, it exhibits small overpotentials of 250 and 100 mV for OER and HER at 10 mA cm−2, as well as good stability. In addition, a small cell voltage of 1.54 V was achieved for overall water splitting at 10 mA cm−2, surpassing that of RuO2+Pt/C catalyst. This work provides a feasible route for designing heterostructure catalysts for water splitting.

Hierarchical Superhydrophilic/Superaerophobic Ni3S2/VS2 Nanorod-Based Bifunctional Electrocatalyst Supported on Nickel Foam for Overall Urea Electrolysis.

The design and preparation of effective nonprecious metal-based catalysts for the urea oxidation reaction (UOR) coupled with the hydrogen evolution reaction (HER) are of great significance to solve both energy shortage and environmental pollution problems. In this study, a novel hierarchical superhydrophilic and superaerophobicity three-dimensional nanorod-like bifunctional catalyst with a heterostructure (Ni3S2/VS2) was prepared on nickel foam via a simple one-step hydrothermal method, serving as an excellent electrocatalyst for both UOR and HER. The formed heterostructure significantly alters the electronic structure, optimizing charge transfer and increasing the number of active sites, which enhances the electrocatalytic performance of Ni3S2/VS2. As a result, this catalyst requires an extremely low potential of 1.396 V at the current density of 100 mA cm-2 for UOR and only 164 mV overpotential at -10 mA cm-2 for HER. Notably, a constructed two-electrode electrolyzer system (Ni3S2/VS2∥Ni3S2/VS2) demonstrates extraordinary activity and long-term stability, achieving a current density of 10 mA cm-2 at a low cell voltage of 1.48 V, which is superior to majority of the reported catalysts. This work demonstrates that the formation of heterostructures can effectively enhance the catalytic activity of nanomaterials toward UOR and HER and provides a feasible strategy for fabricating highly efficient nonprecious metal overall urea electrocatalysts.

Modulated electronic structure of atomic W-doped NiO/Cr2S3 nanotube heterostructure on nickel foam for enhanced overall water splitting

Critical for advancing hydrogen energy industrialization is the need to engineer durable and highly active non-precious electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER). In this study, we developed a novel approach to construct a vertically grown W-doped NiO/Cr2S3 nanotube heterostructure on nickel foam (referred to as tube W-NiO/Cr2S3/NF). This heterostructure serves as an efficient and bifunctional electrocatalyst for overall water splitting through a combination of electrodeposition and etching processes. Our systematic investigations revealed that W-doping effectively induces modifications in the electronic structure of NiO/Cr2S3, thereby boosting its intrinsic activities. Density functional theory reveals that catalytic activity for HER is influenced by the energy states of active valence dz2 orbitals. After W-doping, the resulting antibonding state orbital's unique property, neither completely empty nor fully filled, leads to an ideal hydrogen adsorption energy. Consequently, tube W-NiO/Cr2S3/NF exhibits significantly enhanced performance for overall water splitting. As a bifunctional electrode, tube W-NiO/Cr2S3/NF demonstrates remarkable activity, achieving a cell voltage of 1.58 V at a current density of 10 mA cm−2 for overall water splitting. Furthermore, it exhibits outstanding stability over 100 h in a 1.0 M KOH solution, outperforming commercial Pt-C and IrO2 counterparts.

Interfacial Regulation of Rice-Grain-like Iron-Nickel Phosphide Nanorods on Phosphorus-Doped Graphene Architectures as Bifunctional Electrocatalysts for Water Splitting.

The design of bimetallic metal-organic frameworks (MOFs) with a hierarchical structure is important to improve the electrocatalytic performance of catalysts due to their synergistic effect on different metal ions. In this work, the catalyst comprises bimetallic iron-nickel MOF-derived FeNi phosphides, intricately integrated with phosphorus-doped reduced graphene oxide architectures (FeNi2P-C/P-rGA) through the hydrothermal and phosphating treatments. The hierarchical architecture of the catalyst is beneficial for exposing active sites and facilitating electron transfer. The FeNi2P-C/P-rGA catalyst exhibits excellent performance in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline electrolytes. Notably, FeNi2P-C/P-rGA requires only the overpotential of 93 and 210 mV to achieve a current density of 10 mA cm-2 for the HER and OER with small values of Tafel slope and charge transfer resistance, respectively. Furthermore, the catalyst exhibits boosted activity for overall water splitting with a low potential of 1.56 V. This work can be considered to extend the design of multilevel catalysts in the application of water splitting.