Bifunctional Electrocatalysts Research Articles

Mn‐Doped CoFeP Nanosheets as Effective Electrocatalysts for Superior Overall Water Splitting

For green hydrogen, the exploitation of advanced electrocatalysts is crucial, and transition metal phosphides have great potential in water splitting due to their abundant reserves and optimized electronic structure. Herein, a synergistic approach involving Mn doping and phosphorization is applied to CoFe‐layered double hydroxide nanoflowers to produce a series of bifunctional catalysts Mn‐doped CoFeP (Mn‐CoFeP). Electrochemical evaluations demonstrate that the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance of Mn(10%)‐CoFeP both have notable improvement in 1 M KOH, with the overpotentials of only 160 and 239 mV to achieve current densities of 10 and 100 mA cm−2, respectively. Comparative electrocatalytic analysis indicates that moderate Mn doping mainly contributes to improve the OER performance, while the phosphorization significantly enhances the HER activity, resulting in effective bifunctional catalysis. For overall water decomposition, a total hydrolysis electrolysis cell equipped with the Mn(10%)‐CoFeP bifunctional catalyst requires only 1.64 V to reach a current density of 10 mA cm−2. Furthermore, it performs stable operation for 10 h at a current density of 10 mA cm−2 with a current maintenance rate of 83.6%. This work offers new insights into preparing effective bifunctional electrocatalysts, advancing clean energy development.

Partial Selenization Strategy for Fabrication of Ni0.85Se@NiCr-LDH Heterostructure as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting.

NiCr-LDH and its partial selenization as Ni0.85Se@NiCr-LDH heterostructure is established here as an alkaline water electrolyzer for achieving enhanced overall water splitting efficiency. The hydrothermally synthesized optimized batch of Ni0.85Se@NiCr-LDH is thoroughly characterized to elucidate its structure, morphology, and composition. Compared to pristine NiCr-LDH, the batch of Ni0.85Se@NiCr-LDH exhibits exceptional alkaline OER and HER activity with low overpotentials of 258 and 85 mV at 10 mA cm-2, respectively. Besides, Ni0.85Se@NiCr-LDH also exhibits excellent acidic HER with an overpotential of only 61 mV at 10 mA cm-2, indicating that Ni0.85Se@NiCr-LDH can operate effectively across a wide pH range. The excellent electrochemical stability of Ni0.85Se@NiCr-LDH for 24 h operation is attributed to the formation of a thin layer of SeOx during OER operation. The role of selenization and the effect of Cr in the LDH lattice toward enhanced electrocatalytic water splitting is discussed. The outstanding OER and HER performances of Ni0.85Se@NiCr-LDH are attributed to the higher electrochemical active surface area, favorable conditions for adsorption of HER/OER intermediates, low charge transfer resistance, and improved conductivity. The practical application ofNi0.85Se@NiCr-LDHas a bifunctionalelectrocatalyst for overall water splitting is reflected from the low cell voltage of 1.548 V at 10 mA cm-2.

Enhanced Electrocatalytic Capacity of Two POM@NH2‐MIL‐101(Fe) Composites for Oxygen Evolution Reaction

AbstractThe development and exploration of efficient bifunctional electrocatalysts for water splitting are in high demand and have garnered significant attention in recent years. Herein, by incorporating the advantages of catalytically active polyoxometalates (POMs) and structural stable metal–organic frameworks (MOFs), two POM@MOFs composite materials, Ni4Mo12@Fe and Co4Mo12@Fe, have been successfully prepared via the encapsulation of POMs anions, [MoV12O30(μ2‐OH)10H2{NiII4(H2O)12}]∙14H2O (noted as Ni4Mo12) and [MoV12O30(μ2‐OH)10 H2{CoII(H2O)3}4]∙12H2O (noted as Co4Mo12), into the cavities of MOFs NH2‐MIL‐101(Fe), respectively. Compared to each individual components, Ni4Mo12@Fe and Co4Mo12@Fe composites, as heterogeneous electrocatalysts, both showed enhanced electrocatalytic capacities for efficient oxygen evolution reaction (OER) under alkaline conditions with overpotentials of 332.64 mV for Ni4Mo12@Fe and 352.64 mV for Co4Mo12@Fe at 10 mA cm−2. Additionally, the enhanced electrocatalytic capacities of these two composites could also achieve towards hydrogen evolution reaction (HER). Such a POMs‐assisted strategy for the formation of POM@MOFs composites, described here, paves a new avenue for the development of highly economical, active nonnoble metal bifunctional electrocatalysts for OER and HER.

Ultra-fast synthesis of transition metal-MXene nanocomposite electrocatalyst for energy-saving seawater hydrogen production: Experiment and theory

Switching from the urea oxidation reaction (UOR) to the oxygen evolution reaction (OER) is a beneficial way to lower the amount of energy needed to make hydrogen gas during the hydrogen evolution reaction (HER). Due to the sluggish reaction kinetics of the six electrons reaction of UOR, designing a privileged bifunctional electrocatalyst for both HER and UOR necessitates. The 2D nano-sized non-noble metal electrocatalysts make it possible to speed up reactions and improve their electrocatalytic performance. We synthesized nickel-cobalt-MXene composite nanosheets (NiCoMXene) on the surface of copper foam using a one-pot, simple, and ultra-fast electrochemical method. This 2D electrocatalyst demonstrates high electrocatalytic performance towards HER (overpotential of 76 mV at −10 mA cm−2) with excellent durability in alkaline media. Furthermore, NiCoMXene nanocomposite served as a bifunctional electrocatalyst to investigate hydrogen gas production by a hybrid system HER coupled with UOR in seawater. The NiCoMXene requires a low overpotential for HER (81 mV) and UOR (1.38 V) to achieve a current density of 10 mA cm−2 in seawater, and the needed cell voltage to reach the same current density is 1.42 V in seawater. Our DFT analysis found a significant synergy between MXene and NiCo in the electrocatalyst. PDOS analysis showed remarkably that introducing Ni atoms to MXene shifts the d-band center to the left (lower energy), while Co atoms shifts it to the right (higher energy) and increased states near the Fermi level. This electronic structure makes the nanocomposite an ideal electrocatalyst, with MXene providing electrons and Co atoms serving as active sites for both HER and UOR.This research work can provide a useful directive to explore the electrocatalysts with outstanding catalytic activity.

Maximizing Bifunctionality for Overall Water Splitting by Integrating H2 Spillover and Oxygen Vacancies in CoPBO/Co3O4 Composite Catalyst

In the pursuit of utilizing renewable energy sources for green hydrogen (H2) production, alkaline water electrolysis has emerged as a key technology. To improve the reaction rates of overall water electrolysis and simplify electrode manufacturing, development of bifunctional electrocatalysts is of great relevance. Herein, CoPBO/Co3O4 is reported as a binary composite catalyst comprising amorphous (CoPBO) and crystalline (Co3O4) phases as a high‐performing bifunctional electrocatalyst for alkaline water electrolysis. Owing to the peculiar properties of CoPBO and Co3O4, such as complementing Gibbs free energy values for H‐adsorption (ΔGH) and relatively smaller difference in their work functions (ΔΦ), the composite exhibits H2 spillover (HS) mechanism to facilitate the hydrogen evolution reaction (HER). The outcome is manifested in the form of a low HER overpotential of 65 mV (at 10 mA cm−2). Moreover, an abundant amount of surface oxygen vacancies (Ov) are observed in the same CoPBO/Co3O4 composite that facilitates oxygen evolution reaction (OER) as well, leading to a mere 270 mV OER overpotential (at 10 mA cm−2). The present work showcases the possibilities to strategically design non‐noble composite catalysts that combine the advantages of HS phenomenon as well as Ov to achieve new record performances in alkaline water electrolysis.

Structural and Phase Engineering of a Hierarchical 2D-2D Nickel MOF/Hydroxide-Derived Ni0.85Se/NiTe2 Heterointerface for Robust HER, OER, and Overall Water Splitting.

The development of a nonnoble metal-based cost-effective, efficient, and durable bifunctional electrocatalyst is crucial to achieving the goal of carbon neutrality. In this study, a structural and interfacial engineering approach is employed to design a 2D-2D hierarchical nickel MOF/nickel hydroxide-derived nickel selenide/nickel telluride dual-phase material through a single-step selenotellurization process. The rational design of highly ordered nanoarchitectures provides well-defined voids and ample pathways for ion diffusion. Furthermore, hierarchical nickel selenide/nickel telluride works synergistically at heterojunctions, providing a local ion enrichment mechanism for the catalytic process. As a result, Ni0.85Se/NiTe2@Ni-NH@CC needs an overpotential of 69 and 240 mV to deliver a current density of 10 mA cm-2 for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, with an outstanding stability observed for over 100 h. Moreover, the Ni0.85Se/NiTe2@Ni-NH@CC (+, -) device exhibits excellent overall water-splitting performance with a cell voltage of 1.50 V at 10 mA cm-2 and can be operated steadily for >100 h at 100 mA cm-2. Density functional theory (DFT) calculations indicate favorable kinetics for H-adsorption at the selenotelluride heterojunction, thereby promoting the HER. This work highlights a new approach for designing a unique nanoarchitecture of MOF/hydroxide-derived selenotelluride heterojunctions for high-efficiency energy conversion applications.

Selective Self‐Assembly of Atomically Dispersed Iron and Cobalt Dual Atom Catalyst on Anisotropic Mesoporous Carbon Particles for High Performance Seawater Batteries

AbstractNa‐seawater batteries (SWBs) are environmentally friendly energy storage system that utilizes abundant seawater as an electrolyte alternative to conventional distilled water‐based and organic electrolytes. To achieve high energy efficiency in Na‐SWBs, it is necessary to enhance the activity of bifunctional oxygen electrocatalysts. In this study, an atomically dispersed iron and cobalt dual‐atom nitrogen‐doped lens‐shaped mesoporous carbon (FeCo‐LMC) particles is synthesized as a SWB cathode material using the spinodal decomposition of the polymer blend and selective precursor positioning. The well‐aligned mesoporous structure and synergetic effect of the dual‐atom site realize FeCo‐LMC as a comparable bifunctional oxygen catalyst with the lowest overpotential difference (EOER−EORR) among the other catalysts with natural seawater electrolyte. When applied to the SWB system, the FeCo‐LMC shows a highly improved charge/discharge performance compared to Pt/C and a stable cycling performance for 200 h. Density functional theory calculations reveal the enhanced oxygen catalytic activity of FeCo‐LMC owing to electron delocalization and d‐band center adjustment of FeN4–CoN4 structure.

Targeted Topological Routine Regulation of RuNiOx Precursors for Excellent Alkaline Overall Water Splitting

Designing efficient and stable electrocatalysts for the hydrogen and oxygen evolution reactions (HER and OER) is crucial for green hydrogen production via the water‐splitting system. The bifunctional electrocatalyst offers a promising strategy due to the simplified preparation process and reduced expenses. However, the single‐component bifunctional catalysts often struggle to match the redox potential of water and to achieve proper adsorption/desorption of Gibbs free energy for both H and O intermediates simultaneously. Herein, through precisely controlling the topological transformation path of the RuNiOx precursor, we successfully prepared high‐performance RuNi/Ni and Ru/NiO heterostructure electrocatalysts for the HER and OER, respectively. The energy level matching between the fabricated electrocatalyst and water oxidation/reduction potential confirms the feasibility of HER and OER. The synergistic effect between the active sites ensures rapid, intermediate adsorption/desorption kinetics. As a result, the assembled alkaline overall water splitting setup achieves a current density of 1 A cm‐2 at 2 V and maintains stable operation at 100 mA cm‐2 for 100 hours.

Role of Surfactants on Electrocatalytic Activity of Co/Al Layered Double Hydroxides For Hydrogen and Oxygen Generation

AbstractLayered double hydroxides (LDHs) have recently attracted much attention in the scientific community as a prominent catalyst for oxygen evolution reaction (OER) because they are economical, extremely stable, and highly active. Literature on LDH alone and their hybrids for catalyzing water oxidation are readily available, but LDH catalyzing hydrogen evolution reaction (HER) is meager. Here, we synthesized Co/Al‐based LDH systems that efficiently perform as bifunctional electrocatalysts for both HER and OER. Exfoliation of this layered material via anion intercalation into a few layers further enhanced its activity. In this work, we reported the synthesis of Co/Al LDHs via coprecipitation followed by hydrothermal method and different surfactant‐functionalized LDHs (with anionic surfactant: SDS, cationic surfactant: CTAB, and nonionic surfactant: PEG 4000). SDS‐modified LDH (s LDH) showed notable stability and competent results in hydrogen evolution in addition to oxygen evolution. The exfoliation of s LDH caused enhancement in the high specific surface area about 6.8 times compared to pristine LDH, as evident from BET data. The onset potential for HER as obtained from the polarization curve for s LDH is −0.41 V versus RHE, with Tafel slope of 67.4 mV/dec. Similarly, OER onset potential and corresponding Tafel slope are 1.53 V versus RHE at 10 mA/cm2 and 90.2 mV/dec, respectively.

Enhancing Oxygen Reduction Reaction Electrocatalytic Performance of Nickel‐Nitrogen‐Carbon Catalysts through Coordination Environment Engineering†

Comprehensive SummarySingle‐atom catalysts (SACs) have attracted significant attention due to their high atomic utilization and tunable coordination environment. However, the catalytic mechanisms related to the active center and coordination environment remain unclear. In this study, we systematically investigated the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalytic activities of NiN4, NiN3, NiN3H2, NiN4X, NiN3X, and NiN3H2X (X denotes axial ligand) through density functional theory (DFT) calculations. This study unveils two distinct reaction pathways for ORR and OER, involving proton‐electron pairs adsorbed from both the solution and the catalyst surface. The overpotential is the key parameter to evaluate the catalytic performance when proton‐electron pairs are adsorbed from the solution. NiN3 and NiN3H2 show promise as pH‐universal bifunctional electrocatalysts for both ORR and OER. On the other hand, when proton‐electron pairs are adsorbed from the catalyst surface, the reaction energy barrier becomes the crucial metric for assessing catalytic activity. Our investigation reveals that NiN3H2 consistently exhibits optimal ORR activity across a wide pH range, regardless of the source of proton‐electron pair (solvent or catalyst surface).

Bamboo-derived aerogel with atomically dispersed Co as a high-performance bifunctional electrocatalyst for durable zinc-air batteries

The development of highly efficient and durable bifunctional electrocatalysts is crucial for rechargeable zinc-air batteries, which have garnered significant attention as a promising sustainable energy storage technology. Herein, a novel Co-N-C-1050 catalyst is synthesized using a high-temperature gas transport method, where high purity cobalt powder and bamboo biomass aerogel are treated with ammonia gas at 1050 °C. The resulting catalyst exhibits a 3D interconnected porous network composed of dense carbon fibers, which atomically dispersed Co, N, and C elements are uniformly distributed. The synergistic integration of highly active Co single atoms and N-doped 3D carbon fiber aerogel enables Co-N-C-1050 to demonstrate excellent bifunctional electrocatalytic performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), comparable to commercial Pt/C and RuO2 catalysts. This catalyst has a half-wave potential of 0.842 V for ORR and a potential of 1.472 V at 10 mA cm−2 for OER, outperforming N-C-1050 and benchmark catalysts. A zinc-air battery is driven by Co-N-C-1050 achieves a high power density of 135 mW/cm2 and exceptional stability over 138 h of charge/discharge cycling, surpassing the higher-cost Pt/C + RuO2 catalyst. This biomass aerogel based single-site Co-N-C catalyst offers a promising approach for developing high-efficiency and long-cycle-life zinc-air batteries.

Theoretical Investigation of Single-, Double-, and Triple- p-block Metals Anchored on g-CN Monolayer for Oxygen Electrocatalysis.

The design and development of highly active non-noble metal electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are crucial for metal-air batteries. In this work, the electrocatalytic performance of different p-block metal (PM = Sn, Sb, Pb and Bi) atoms embedded in the g-CN monolayer (PMx@g-CN, x = 1-3) for the OER and ORR was systematically investigated by density functional theory (DFT). The strong interaction between PMx atoms and g-CN substrates indicates the good stability of PMx@g-CN catalysts. Among all the designed catalysts, Bi3@g-CN is found to be a promising bifunctional electrocatalyst for both the OER and ORR with the calculated overpotential ηOER and ηORR of 0.23 and 0.25 V, respectively. With the atomic active sites of PMx increasing from x = 1 to 3, the OER and ORR catalytic activity is enhanced. The correlations between the overpotentials of the OER/ORR and Bader charge values of the anchored PMx atoms of the catalysts were established. Our findings contribute to searching for noble metal-free bifunctional electrocatalysts and shed light on the rational design of atomic active sites on electrocatalysts.

Cobalt Phosphide Decorating Metallic Cobalt With a Nitrogen‐Doped Carbon Nano‐Shell Surpasses Platinum Group Metals for Oxygen Electrocatalysis Applications

ABSTRACTIt has been a long‐standing challenge to cultivate capable and resilient oxygen electrocatalysts with higher activity, low price, and long lifetime to replace the commonly used platinum group metals, i.e., Pt for oxygen reduction reaction (ORR) and RuO2/IrO2 for oxygen evolution reaction (OER). This work presents a promising approach to address the challenges associated with oxygen electrocatalysis by introducing a cobalt phosphide/metallic cobalt (Co2P/Co) core wrapped in a nitrogen‐doped conductive carbon (CN) nano‐shell, demonstrated as Co2P/Co@NC. The strong chemical bonding between metallic cobalt and phosphorus, nitrogen and conductive carbon contributes to the enhanced conductivity and stability of the electrocatalyst. The nitrogen doping in the carbon shell provides additional Co–N active sites, which are crucial for ORR activity. Co2P/Co@NC demonstrates promising activity and stability compared to noble metals such as Pt for ORR in an alkaline medium. This suggests its potential as a cost‐effective alternative to Pt‐based catalysts. Further, due to factors such as strong cobalt‐phosphide bonding, high cobalt oxidation states and excellent conductivity of the nitrogen‐doped carbon shell, the Co2P/Co@NC outperforms noble metal oxides like iridium dioxide (IrO2) and ruthenium dioxide (RuO2) for OER. Co2P/Co@NC exhibits a low potential difference of 0.63 V, which is among the lowest reported for bifunctional electrocatalysts capable of both ORR and OER. Overall, the described strategy offers a promising avenue for developing efficient, low‐cost and stable electrocatalysts for oxygen reactions, which are crucial for various electrochemical energy conversion and storage technologies, such as fuel cells and metal–air batteries.

Enabling High‐Rate and Long‐Cycling Zinc–Air Batteries with a ΔE = 0.56 V Bifunctional Oxygen Electrocatalyst

AbstractZn–air batteries (ZABs) are promising next‐generation energy storage devices due to their low cost, intrinsic safety, and environmental benignity. However, the sluggish kinetics of the cathodic reactions severely limits the ZAB performances in practical use, calling for high‐efficiency bifunctional oxygen reduction and evolution electrocatalysts. Herein, an ultrahigh‐active bifunctional electrocatalyst is developed with a record‐low ΔE of 0.56 V, significantly outperforming the noble‐metal‐based benchmark (Pt/C+Ir/C, ΔE = 0.77 V) and many other reported bifunctional electrocatalysts (mostly ΔE ≥ 0.60 V). The nanoscale composite of Fe‐based single‐atom sites and nanosized layered double hydroxides endows the bifunctional electrocatalyst with high conductivity and a large active surface that afford strengthened electron conduction and ion transport pathways. Furthermore, a remarkable improvement in stability is realized following the current division principle. ZABs with the bifunctional electrocatalyst deliver a high peak power density of 198 mW cm−2 and excellent cycling durability for over 6000 cycles. Moreover, ampere‐hour‐scale ZABs are constructed and cycled under 1.0 A and 1.0 Ah conditions. This work breaks the activity record for bifunctional oxygen electrocatalysis and expands the potential of ZABs for sustainable energy storage.

N/S‐codoped Nickel oxide supported on activated Montmorillonite clay as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Developing low‐cost, highly effective, and durable electrocatalysts for complete water splitting (OER/HER) is crucial for future energy provision. Herein, we report N/S‐codoped Nickel oxide supported on activated Montmorillonite clay as an efficient bifunctional electrocatalyst for water electrolysis. The different wt% of Ni‐MMT catalysts were synthesized using an effortless one‐step solvothermal method and their phase recognition, morphology, analysis of elements, and electrochemical performance were confirmed by various characterization techniques. The optimal 10 Ni‐MMT catalyst exhibits outstanding efficiency in both HER (170 mV) and OER (365 mV) at a current density of 10 mAcm‐2 in 1M KOH. Furthermore, doping of N/S heteroatoms increases the active sites for HER/OER, facilitates charge transfer and achieves electrochemical stability of 15 h. The Ni‐MMT catalyst achieved an overall water‐splitting performance in 1M KOH, reaching 10 mAcm‐2 at a cell voltage of 1.82 V.

Deep eutectic solvent-mediated synthesis of CuCo2O4 @ Sargassum tenerrimum derived carbon heterostructure as an efficient electrocatalyst for oxygen and hydrogen evolution reactions

Developing bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) through simple, economical, and innovative methods is vital for sustainable energy conversion. Here, we showcase a green and sustainable approach for synthesizing CuCo₂O₄ - Sargassum Tenerrimum derived carbon composites (CCST) directly from fresh seaweed and a deep eutectic solvent (DES), marking its initial application in HER/OER. The successful transformation of seaweed and metal precursors into CCST was accomplished using a direct pyrolysis method at 900 °C in an inert atmosphere. Here, Seaweed granules acted as the carbon source, with DES employed for its multifunctional properties, including serving as a solvent, a structural template, and a catalyst for fostering material development. When these materials were assessed as electrocatalysts for OER in 1 M KOH media, the optimal catalyst (CCST-9 (1:2)) exhibited a low overpotential of 381 mV at 10 mA cm−2 with a Tafel slope of 44 mV dec−1. In addition, the same material achieved low overpotential of 383 mV at 10 mA cm−2 with a Tafel slope of 100 mV dec−1 when tested as an electrocatalyst for HER in 0.5 M H2SO4 media. Interestingly, CCST-9 (1:2) demonstrated excellent long-term stability in OER in 1 M KOH during a 24-h chronoamperometry test, with only a minor reduction in current density. The present study contributes new perspectives to the development of scalable and high-performance bifunctional catalysts, achieved through an environmentally friendly and cost-effective synthetic strategy.

Benchmarking overall water splitting performance of heterostructured Fe-doped NiMo/NiCo@NF bifunctional electrocatalyst

The design of high-efficiency and cost-effective electrocatalysts for water splitting has recently received much attention. Herein, a self-supported Fe-doped NiMo/NiCo bifunctional electrocatalyst was synthesized using hydrothermal method on nickel foam (NF) to enhance both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). SEM observations revealed NiCo microspheres arranged in a flower-like structure, with Fe-doped NiMo rods decorating the surface. This electrocatalyst demonstrated impressive HER performance, requiring a low overpotential of 63 mV, versus reversible hydrogen electrode (RHE), at a cathodic current density of -10 mA/cm2, and a small charge transfer resistance (Rct) of 2.43 Ω at -200 mV (RHE). For OER, the synthesized electrocatalyst revealed an excellent activity, with a low overpotential of 151 mV (RHE) to afford an anodic current density of 10 mA/cm2 and a small Rct of 0.43 Ω at 300 mV (RHE). Meanwhile, the Fe-doped NiMo/NiCo@NF electrocatalyst in a two-electrode configuration needed only a cell voltage of 1.53 V to deliver a current density of 10 mA/cm2. Overall, this work disclosed that the combination of NiCo and NiMoFe results in the synthesis of a heterogeneous electrocatalyst that offers high efficiency for water splitting and maintains good stability over 10 h.

Spherical Ru/FeOx composite as a bifunctional electrocatalyst for overall water splitting in neutral media

Electrochemical water splitting stands out as a promising technology for H2 production, due to its simplicity and high energy conversion efficiency. Therefore, it is a key issue to develop and design efficient catalysts for overall water splitting (OWS), especially in neutral media. Herein, the present study presents a stable bifunctional electrocatalyst, namely a spherical structure consisting of ruthenium and iron oxide composite supported on iron foam (Ru/FeOx), which was prepared using a simple two-step process. In 1.0M PBS, the optimized Ru/FeOx-300 demonstrates low overpotentials of 30 and 212mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at 10mAcm-2, respectively. More impressively, Ru/FeOx-300 requires only 1.505V to achieve a current density of 10mAcm-2 and exhibits superior electrochemical stability for 24h in a two-electrode neutral electrolyzer. The outstanding catalytic performance and stability of Ru/FeOx-300 nanospheres for water splitting are attributed to the binder-free integrated structure, the enhanced charge transfer facilitated and the synergistic effect between Ru and FeOx. This study offers a novel approach to the development of high-efficiency electrocatalysts for overall water splitting in neutral media.

Boosting the catalytic performance of carbon nitrides for overall water splitting by tuning the C/N ratio: A theoretical investigation

We systematically study the catalytic activity of carbon nitride materials by controlling the carbon-to-nitrogen ratio and engineering their morphological structure. The electrocatalytic activities of five types of carbon nitrides with different C/N ratios— C4N, C3N, C2N, CN, and C3N4 — toward the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are theoretically evaluated. The results show that the OER overpotential decreases as the nitrogen content increases, reaching its lowest value in CN. Our results highlight CN as a bifunctional electrocatalyst with acceptable performance with overpotentials of 0.76 and 0.05 V for OER and HER, respectively.

Porous and defective NiCo2O4 spinel derived from bimetallic NiCo-based Prussian blue analogue for enhanced hydrogen production via the urea electro-oxidation reaction

The efficient hydrogen production via overall water splitting is seriously restrained by the slow kinetics of the oxygen evolution reaction (OER). The substantially low potential for the urea electro-oxidation reaction (UOR) can tackle this problem by replacing the OER at the electrolyzer anode. Herein, the NiCo2O4 spinel with rich oxygen vacancies (Ov) and embedded within mesoporous carbon network (Ov-NiCo2O4@mC) was derived from NiCo-based Prussian blue analogous (NiCo PBA) and exploited as the bifunctional electrocatalyst of the UOR and OER for boost the hydrogen production via the overall water splitting. Benefiting to the regular skeleton and abundant dual metal sites of NiCo PBA, the derived Ov-NiCo2O4@mC comprises abundant oxygen vacancies, lattice defects, and adjustable electron structure. These features afford Ov-NiCo2O4@mC the improved UOR ability, showing the potential of 1.33 V versus reversible hydrogen electrode (RHE) at the current density of 10 mA cm−2, along with a small Tafel slopes of 31 mV dec-1, remarkably lower than that of the OER (1.51 V versus RHE, Tafel slope = 85 mV dec-1). The UOR performance of Ov-NiCo2O4@mC substantially outperforms to most of the reported Co and/or Ni-based electrocatalysts. Impressively, the assembled two-electrode urea-assisted overall water splitting device shows the small voltage for the hydrogen production (1.43 V versus RHE) and good long-term stability. The present work can provide a new alternative for the efficient hydrogen production using the MOFs-derivatives.