Oxygen Evolution Reaction Overpotential Research Articles

Customized structure engineering of MIL-53(Fe)/MoS2/NF for enhanced OER performance: Experiments and practical applications

Developing cost-effective and highly efficient catalysts to replace the expensive noble metal-based counterparts in the oxygen evolution reaction (OER) holds paramount importance for the advancement of hydrogen production. Herein, we synthesized a novel hybrid composite of MIL-53(Fe) and MoS2 using a hydrothermal method, subsequently depositing it onto commercially available nickel foam (NF), namely MIL-53(Fe)/MoS2/NF. The MIL-53(Fe)/MoS2/NF composite capitalizes on the synergies among these three components, facilitating efficient water electrolysis while remarkably curbing the OER overpotential (η10 = 238 mV, 1 M KOH), thereby enhancing electron transport efficiency. Remarkably, the OER overpotential remains consistently low even in the prepared 1 M KOH solution using seawater (η10 = 289 mV) and sewage (η10 = 301 mV). Moreover, MIL-53(Fe)/MoS2/NF exhibits enduring stability, maintaining its efficacy even after 50 h at around 50 mA/cm2 in simulated solutions, sewage, and seawater. In an electrolytic cell utilizing MIL-53(Fe)/MoS2/NF as the anode, stable gas production is achieved under 1 M KOH conditions and solar cell voltages of 1.62 V and 1.85 V. This investigation marks a pivotal advancement in forging highly efficient and economically viable OER catalysts, holding substantial implications for advancing energy conversion methodologies, thereby ushering in escalated efficiency and diminished costs.

Mesoporous RE0.5Ce0.5O2-x Fluorite Electrocatalysts for the Oxygen Evolution Reaction.

Developing highly active and stable electrocatalysts for the oxygen evolution reaction (OER) is key to improving the efficiency and practical application of various sustainable energy technologies including water electrolysis, CO2 reduction, and metal air batteries. Here, we use evaporation-induced self-assembly (EISA) to synthesize highly porous fluorite nanocatalysts with a high surface area. In this study, we demonstrate that a 50% rare-earth cation substitution for Ce in the CeO2 fluorite lattice improves the OER activity and stability by introducing oxygen vacancies into the host lattice, which results in a decrease in the adsorption energy of the OH* intermediate in the OER. Among the binary fluorite compositions investigated, Nd2Ce2O7 is shown to display the lowest OER overpotential of 243 mV, achieved at a current density of 10 mA cm-2, and excellent cycling stability in an alkaline medium. Importantly, we demonstrate that rare-earth oxide OER electrocatalysts with high activity and stability can be achieved using the EISA synthesis route without the incorporation of transition and noble metals.

Interface effect of MXene/CoP2 on oxygen evolution reaction

Zero/two-dimension MXene/CoP2 was fabricated by hydrothermal and chemical vapor deposition phosphate. MXene nanosheets were employed as substrate to increase dispersion and stability of the multicomponent catalyst. The morphology of CoP2 was regulated by the addtion of Co precursor in hydrothermal process. The catalyst prepared by 40 mg MXene with 0.5 mmol Co precursor (MXene/CoP2-0.5) showed a uniform growth of CoP2 and formed aboundant reaction sites. The interfacial electron transfer between MXene and CoP2 modulated the electron structure of CoP2 and stimulated the oxygen evolution reaction (OER) activity. The optimized MXene/CoP2-0.5 exhibited the OER overpotential of 263 mV and a long-term stability over 16 h. Modulating the interfacial electron transfer of multicomponent catalysts provided a guidance for electrocatalyst design and synthesis.

Precisely controlled electronic state of Fe-Ni3P electrocatalyst via moderate phosphorization for urea-assisted overall water splitting

Phosphorization process is one of the most practical and efficient way for electronic modification of transition metals. However, achieving precise control on the electronic states of transition metal catalysts is difficult during phosphorization process for remarkable catalytic capacities in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we provided a novel method of precisely adjusting the electronic states of Ni and Fe via moderate phosphorization process, which exerts the synergistic effect between the electroactive elemental Fe and Ni3P species. The transformation of Ni to Ni3P and preservation of elemental Fe via moderate phosphorization were of significant essence for the electrocatalytic advances towards HER and OER processes. The density of theory (DFT) calculations showed that the total density of states (TDOS) of Fe/Ni3P (moderate phosphorization) is more than 2.5 times higher than that of FeP/Ni2P (complete phosphorization). Simultaneously, the Fe contribution to the TDOS in the form of FeP is 6 times less than that in the form of Fe element and the Ni contribution in the form of Ni2P is also not competitive with that in the form of Ni3P. The resulting Fe-Ni3P@NF-2P electrocatalyst exhibits 208 and 239 mV OER overpotentials at 10 and 100 mA cm-², as well as 137 mV for HER at 10 mA cm-². A 1.567 V cell voltage was required to electrochemically decompose water at 10 mA cm-². Surprisingly, by adding 0.33 M urea in the electrolyte, the cell voltage was reduced as low as 1.499 V. We demonstrate a novel approach of preparing electrocatalysts by precisely tuning the electronic properties of metals via moderate phosphorization.

Optimization of Interfacial OH− Accessibility by Constructing a Delayed–Release Membrane Electrode for Ampere–Level Hydrogen Production

AbstractAchieving a high current density during electrochemical overall water splitting is a promising strategy for industrial energy conversion. The mass diffusion rate of OH− ions from the electrolyte to the interfacial active sites strongly influences the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) . Herein, the delayed‐release of OH− ions modulated by a proper organic polymer membrane on the electrode surface can optimize the OH− accessibility to the active sites (as indicated by the molecular dynamics simulations) is demonstrated and that van der Waals interaction force modulates the OH− residence time in the reaction system. The remarkable performance of the membrane‐modified electrode is achieved at ultra‐high current densities of 1.9 A cm−2 (with an HER overpotential of 602 mV) and 2 A cm−2 (with an OER overpotential of 459 mV) in 1 M KOH solution. Consequently, a super‐high current density of 1.3 A cm−2 is obtained for overall water splitting (at a voltage of only 2.2 V), which is 1.9‐fold higher than that of a benchmarked Pt/C‐IrO2 (684 mA cm−2). Therefore, the delayed‐release of OH− has optimized the mass conversion efficiency of the active sites, thus improving the electrochemical performance of overall water splitting.

Pulse electrodeposition synthesis of Ti/PbO2-IrO2 nano-composite electrode to restrict the OER in the zinc electrowinning

Pulsed and constant direct current electrodepositions were applied to synthesize PbO2-IrO2 nano-composites on Ti substrate. By compositing PbO2 with nano-sized IrO2 particles, a suitable anode was prepared for zinc electrowinning that decreases the electrocatalytic activity for oxygen evolution reaction overpotential (OER) while increasing the electrochemical active surface area and the electrocatalytic activity for OER. To provide PbO2-IrO2 nano-composites on Ti substrate with Sb2O3 interlayer, current density, temperature, and time of anodization are optimized using the one-at-the-time method. The optimal condition for the anode involves a DC time of 1 h, incorporating 2 g L-1 of IrO2 nanoparticles, maintaining a current density of 50 mA cm− 2 for the DC mode, and setting the pulse off-time (toff) to 770 ms. Based on the electrochemical evaluations in a simulated zinc electrowinning electrolyte, the effect of IrO2 nanoparticles on the catalytic activity of Ti/β-PbO2 anode for OER was determined. Anodic polarization curves showed that the OER overpotential of PbO2-IrO2 micro-composite and PbO2-IrO2 nano-composites at a current density of 10 mA cm-2 decreased to 0.471 V, respectively, compared to 0.711 V for pure PbO2. The Nyquist plots in the OER zone confirm that the PbO2-IrO2 nano-composite anode exhibits the lowest Rct 2.79 Ω compared to 6.0 Ω and 9.46 Ω for PbO2-IrO2 micro-composite and pure PbO2, which can be attributed to the presence of electro-catalytic IrO2 nanoparticles.

Surface reconstruction of La0.6Sr0.4Co0.8Ni0.2O3-δ perovskite nanofibers for oxygen evolution reaction

Perovskites have become promising alternatives to precious metal-catalyzed oxygen evolution reaction (OER). Herein, we report the synthesis of several perovskite nanofibers, specifically La0.6Sr0.4CoxNi1-xO3-δ (LSCN), and investigate their electrocatalytic water oxidation activity in alkaline electrolytes. La0.6Sr0.4Co0.8Ni0.2O3-δ (LSCN-0.8) is selected and immersed in an aqueous NaBH4 solution for 1 h for surface reconstruction. The perovskite nanofibers' electrocatalytic OER activity and stability are rigorously evaluated using a standard three-electrode system. Results reveal that even a slight Co substitution for Ni content within the LSCN perovskite structure has a notable impact on electrocatalytic activity. Moreover, LSCN-0.8 exhibits an overpotential of 363 mV at 20 mA cm−2 in 1 M KOH. However, significant improvement is observed after the surface reconstruction process. The optimized LSCN-0.8 (now called LSCN-2) displays the lowest OER overpotential (320 mV) under the same conditions. Furthermore, the LSCN-2 nanostructure demonstrates exceptional electrode stability, as evidenced by only a slight decrease in electrocatalytic performance during 5000 cycles of linear sweep voltammetry.

Polypyrrole-wrapped Hofmann type metal–organic framework nanoflowers to boost oxygen evolution reaction

The exploration of efficient and stable metal-organic frameworks (MOFs) for electrocatalytic oxygen evolution reaction (OER) has received increasing attention. However, the limited electronic conductivity of MOFs hinders the electron transfer rate. Herein, we report the preparation of conducting polypyrrole (PPy)-modified MOF nanoflowers (MOF-NFs@PPy) as promising electrocatalysts for OER. The PPy layer significantly increases the electrical conductivity and modulates the ionic transmittance between MOF-NFs and the electrolyte. The interaction of PPy with the MOF-NFs modifies the electronic structure and improves the reaction efficiency at the active sites. The obtained MOF-NFs@PPy exhibits excellent electrocatalytic activity with an OER overpotential of only 218 mV@10 mA cm−2 and small Tafel slope of 47.4 mV dec−1. In addition, the MOF-NFs@PPy exhibited excellent long-term stability (>24 h). This work may provide a new idea and a novel construction strategy for MOFs to improve OER performance.

Oxygen vacancies enhanced electrocatalytic water splitting of P-FeMoO4 initiated via phosphorus doping

Transition metal oxides (TMOs) are abundant and cost-effective materials. However, poor conductivity and low intrinsic activity limit their application in electrolyzed water catalysts. Herein, we prepared P-FeMoO4 in situ on nickel foam (P-FMO@NF) by phosphorylation-modified FeMoO4 to optimize its electrocatalytic properties. Interestingly, phosphorus doping is accompanied by the generation of oxygen vacancies and surface phosphates. Oxygen vacancies accelerated Mo dissolution during the oxygen evolution reaction (OER), leading to the rapid reconfiguration of P-FMO@NF to FeOOH and regulating the electronic structure of P-FMO@NF. The formation of phosphates is caused by the substitution of some molybdates with phosphates, which further increases the amount of oxygen vacancies. Hence, the OER overpotential of P-FMO@NF at a current density of 10 mA cm−2 is only 206 mV, and the hydrogen evolution reaction (HER) overpotential is 154 mV. It was assembled into a water splitting cell with a voltage of just 1.59 V at 10 mA cm−2 and shows excellent stability over 50 h. These excellent electrocatalytic properties are mainly attributed to the oxygen vacancies, which improve the interfacial charge transfer properties of the catalysts. This study provides new insights into phosphorus doping and offers a new perspective on the design of electrocatalysts.

Insights into the electrochemical catalytic mechanism of atomically dispersed metal on h-BCN monolayer.

Exploiting efficient and inexpensive electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of great significance for the rapid development of renewable energy technologies. The embedding of single-atom metals into two-dimensional (2D) carbon-based materials as electrocatalysts for fuel cells and metal-air batteries have become a major research focus. Herein, the catalytic properties of the ORR and OER of partial metal atoms embedded in a two-dimensional h-BCN monolayer were systematically investigated on thermodynamic and kinetic scales using density functional theory calculations. Electronic structure studies confirm that the d orbitals of metal atoms hybridize with the 2p orbitals of the O atom, modulating the adsorption free energies of oxygen-containing intermediates (OOH, O and OH). Comparison and analysis of catalytic activity results reveal that Co single-atom catalysts (Co-SACs@h-BCN) possess the lowest ORR and OER overpotentials and therefore are expected to be a kind of excellent bifunctional electrocatalyst. This study not only demonstrates that boron- and nitrogen-doped carbon-based materials embedded with partial metal atoms are superior 2D electrocatalysts, but also provides guidance for the investigation of efficient non-precious metal-based bifunctional electrocatalysts.

First-principle calculations study of the ORR/OER electrocatalytic activity of ruthenium polyphthalocyanine axially modified with aliphatic thiol groups.

In this study, the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activity of ruthenium polyphthalocyanine axially modified with different aliphatic thiol groups, RuPPc-SR (SR = -SCH3, -SC2H5, -SC3H7, -SC4H9, -SC5H11, and -SC6H13), in an acidic medium were simulated using DFT. All -SR groups can effectively enhance the ORR and OER catalytic activities of RuPPc. The ORR and OER overpotentials of RuPPc-SC4H9 are 0.237 V and 0.436 V, respectively, which are far lower than those of RuPPc (0.960 V and 0.903 V). For RuPPc-SC4H9, the four C and S atoms of the -SC4H9 chain and Ru atom are coplanar, and thus, conjugate effects and inductive effects exist between the -SC4H9 chain and Ru atom. This makes the Ru atom exhibit the least positive Bader charge and smallest spin density, and the anti-bonding orbitals of dxz, dyz, and dz2 of the Ru atom shift below the Fermi level (Ef). This makes the adsorption strength of RuPPc-SC4H9 toward ORR and OER intermediates the weakest, which accelerates the reaction process, thus resulting in better ORR and OER catalytic activity. Therefore, the introduction of the aliphatic thiol groups might effectively improve the OER/ORR catalytic activity of RuPPc.

Perovskite CoSn(OH)6 nanocubes with tuned d-band states towards enhanced oxygen evolution reactions.

The CoSn(OH)6 perovskite hydroxide is a structure stable and inexpensive electrocatalyst for the oxygen evolution reaction (OER). However, the OER activity of CoSn(OH)6 is still unfavorable due to its limited active sites. In this work, an Fe3+ doping strategy is used to optimize the d-band state of the CoSn(OH)6 perovskite hydroxide. The CoSn(OH)6 catalyst with slightly Fe3+ doped nanocubes is synthesized by a facile hydrothermal method. Structure characterization shows that Fe3+ ions are incorporated into the crystal structure of CoSn(OH)6. Owing to the regulation of the electronic structure, CoSn(OH)6-Fe1.8% exhibits an OER overpotential of 289 mV at a current density of 10 mA cm-2 in OER electrochemical tests. In situ Raman spectroscopy shows that no obvious re-construction occurred during the OER for both CoSn(OH)6 and CoSn(OH)6-Fe1.8%. DFT calculations show that the introduction of Fe3+ into CoSn(OH)6 can shift the d-band center to a relatively high position, thus promoting the OER intermediates' adsorption ability. Further DFT calculations suggest that incorporation of an appropriate amount of Fe3+ into CoSn(OH)6 significantly reduces the rate-determining Gibbs free energy during the OER. This work offers valuable insights into tuning the d-band center of perovskite hydroxide materials for efficient OER applications.

Elevated temperature-driven coordinative reconstruction of an unsaturated single-Ni-atom structure with low valency on a polymer-derived matrix for the electrolytic oxygen evolution reaction.

A high-temperature pyrolysis-controlled coordination reconstruction resulted in a single-Ni-atom structure with a Ni-Nx-C structural unit (x = N atom coordinated to Ni). Pyrolysis of Ni-phen@ZIF-8-RF at 700 °C resulted in NiNP-NC-700 with predominantly Ni nanoparticles. Upon elevating the pyrolysis temperature from 700 to 900 °C, a coordination reconstruction offers Ni-Nx atomic sites in NiSA-NC-900. A combined investigation with X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and soft X-ray L3-edge spectroscopy suggests the stabilization of low-valent Niδ+ (0 < δ < 2) in the Ni-N-C structural units. The oxygen evolution reaction (OER) is a key process during water splitting in fuel cells. However, OER is a thermodynamically uphill reaction with multi-step proton-coupled electron transfer and sluggish kinetics, due to which there is a need for a catalyst that can lower the OER overpotentials. The adsorption energy of a multi-step reaction on a single metal atom with coordination unsaturation tunes the adsorption of each oxygenated intermediate. The promising OER activity of the NiSA-NC-900/NF anode on nickel foam was followed by the overall water splitting (OWS) using using NiSA-NC-900/NF as anode and Pt coil as the cathodic counterpart, wherein a cell potential of 1.75 V at 10 mA cm-2 was achieved. The cell potential recorded with Pt(-)/(+)NiSA-NC-900/NF was much lower than that obtained for other cells, i.e., Pt(-)/NF and NF(-)/(+)NF, which enhances the potentials of low-valent NiSAs for insightful understanding of the OER. At a constant applied potential of 1.61 V (vs.RHE) for 12 h, an small increase in current for initial 0.6 h followed by a constant current depicts the fair stability of catalyst for 12 h. Our results offer an insightful angle into the OER with a coordinatively reconstructed single-Ni-atom structure at lower valency (<+2).

Ni-modified Co3O4 with competing electrochemical performance to noble metal catalysts in both oxygen reduction and oxygen evolution reactions

The commercial viability of zinc-air batteries (ZABs) depends upon the availability of cost-effective and high-performance bifunctional electrocatalyst, which can simultaneously accelerate both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Noble metal catalysts suffer from poor cycling stability and cost ineffectiveness. Here we report on a Ni-modified spinel Co3O4 catalyst, which exhibits competing electrochemical properties to Pt/C in ORR and to RuO2 in OER. A ZAB cell fabricated with the catalyst as cathode and Zn as anode exhibits a specific capacity of 803 mAh/g and a cycling stability of 240 h at 5 mA cm−2, comparable to commercial noble metal catalysts. Computational calculations reveal that Ni partially substitutes tetrahedral Co sites in spinel Co3O4 to induce the formation of oxygen vacancies, which play an important role in hindering peroxide formation and enhancing electron conductivity. The presence of Ni in Co3O4 also weakens the interaction between surface Co and OH*, lowering the overpotentials of ORR and OER.

Graphene Architecture-Supported Porous Cobalt-Iron Fluoride Nanosheets for Promoting the Oxygen Evolution Reaction.

The design of efficient oxygen evolution reaction (OER) electrocatalysts is of great significance for improving the energy efficiency of water electrolysis for hydrogen production. In this work, low-temperature fluorination and the introduction of a conductive substrate strategy greatly improve the OER performance in alkaline solutions. Cobalt-iron fluoride nanosheets supported on reduced graphene architectures are constructed by a one-step solvothermal method and further low-temperature fluorination treatment. The conductive graphene architectures can increase the conductivity of catalysts, and the transition metal ions act as electron acceptors to reduce the Fermi level of graphene, resulting in a low OER overpotential. The surface of the catalyst becomes porous and rough after fluorination, which can expose more active sites and improve the OER performance. Finally, the catalyst exhibits excellent catalytic performance in 1 M KOH, and the overpotential is 245 mV with a Tafel slope of 90 mV dec-1, which is better than the commercially available IrO2 catalyst. The good stability of the catalyst is confirmed with a chronoamperometry (CA) test and the change in surface chemistry is elucidated by comparing the XPS before and after the CA test. This work provides a new strategy to construct transition metal fluoride-based materials for boosted OER catalysts.

Self-supporting trimetallic NiCoFe layered-double-hydroxide/amorphous sulfide heterostructure on nickel foam for efficient water splitting

For efficient overall water splitting, a ternary layered double hydroxide (LDH) and sulfide (NiCoFeLDH/NiCoFeS) composite on nickel foam (NF) has been developed as a bifunctional catalytic electrode. The growth of NiCoFeLDH/NiCoFeS–NF catalysts take place employing a three-step process that involves hydrothermal-sulfurization-hydrothermal reaction. Ultrafine nano-needle NiCo(OH)2 is deposited on the NF using a hydrothermal process, followed by immersion in Na2S solution, which ensures its mild conversion to NiCo sulfide. The Fe ions incorporated during the secondary hydrothermal process participate in the dissolution-recrystallization process of the lattice and modify the electronic structure, thereby significantly enhancing endogenous activity. The hetero-structured interface between NiCoFeLDH and NiCoFeS provides additional catalytic reaction sites, improves electronic interactions, and facilitates water dissociation kinetics. NiCoFeLDH/NiCoFeS–NF demonstates improved performance in both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The HER and OER overpotentials are measured to be only 191 and 241 mV at a current density of 100 mA cm−2 in 1 M KOH solution, respectively. Therefore, when NiCoFeLDH/NiCoFeS–NF has been employed as bifunctional electrodes for water splitting, 50 mA cm−2 is reached at only 1.63 V.

Metal–organic framework derived phosphide-hydroxide heterostructure as bifunctional oxygen electrocatalyst for zinc–air batteries

Rational design and fabrication of high-efficiency electrocatalysts is essential for improving the kinetics of both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), so as to constructing high-performance rechargeable zinc-air batteries (ZABs). Among the promising candidates, transition metal-based (oxy)hydroxides have attracted extensive attention for their considerable catalytic potential on oxygen-involved reaction, while unsatisfactory intermediate adsorption/desorption strength and low conductivity limit their practical feasibility. In this work, interface engineering modification strategy is proposed, and a metal–organic framework derived heterostructure catalyst of CoFeOxHy-CoP@CC is fabricated. Comprehensively analyses demonstrate that the interaction between phosphide-(oxy)hydroxide induces the interfacial electronic redistribution, while the formed Schottky heterostructure facilitates rapid electron transfer. All these kinetically favorable for both OER and ORR, and leads to remarkable bifunctional performance on CoFeOxHy-CoP@CC, with the OER overpotential of 240 mV to deliver the current density of 10 mA·cm−2, which is better than CoP@CC, CC and RuO2. In practical applications, liquid zinc-air cells assembled by CoFeOxHy-CoP@CC deliver the peak power density up to 117.55 mW cm−2, which is close to that of 20% Pt/C catalyst (108.48 mW cm−2), and considerable operational performance has also been achieved in all solid-state flexible ZABs.

Designing the major active site of Cu atom for OER via a composite electrocatalyst of Agx@HEO: Experiment and theory

Copper element with low chemical activity is hard to be used as the major active site for oxygen evolution reaction (OER). To improve its OER performance, a specialized structural and chemical environments need be designed. In this work, the composite electrocatalyst of Agn@HEO were synthesized by a simple co-precipitation plus annealing methods. With the aid of the elemental Ag0 atom, part of Cu ions in high entropy oxide (HEO) phases were gradually transferred to the elemental Cu0 atoms and mixed with Ag0 atom for CuAg alloy. This transition evidently altered the chemical environments of Cu element. Thanks to the largest molar percentage of Cu0 atom, the designed Ag1@HEO specimen exhibited the fairly low experimental OER overpotential of 249 (308) mV at the current density of 10 (100) mA cm−2 with the small Tafel slope of 55.2 mV dec-1 and stable electrocatalytic activity. Based on the density functional theory simulation, the theoretical OER overpotential of Cu active site could be adjusted along with the ridges of “volcanic” in both atomic and ionic environments, and achieved the smallest value of 213 mV as the d band center of Cu0 atom had a suitable value near the “volcanic” peak. This design strategy would be adopted to provide an effective enhancement scheme for OER on Cu active site.

NiSe2 nanosheets with electronic structure regulated by Mo-doping as an efficient bifunctional electrocatalyst for overall water splitting

Developing low-cost, highly efficient and stable bifunctional electrocatalysts for overall water splitting is vital but still a challenge. Hetero-atom doping is an effective strategy to improve the catalytic activity of electrocatalysts by increasing active sites and regulating electronic structure. Here, Mo-doped NiSe2 nanosheets were in situ grown on nickel foam (NF) by hydrothermal and the subsequent selenization process as bifunctional electrocatalysts for overall water splitting. Incorporation of Mo into NiSe2 can regulate the electronic structure, increase the numbers of high-valence Ni3+ and active sites, generate the disorder defects due to the formation of active material NiOOH, and decrease the charge transfer resistance. The above synergistic roles make the Mo-doped NiSe2 to present superior catalytic performances and remarkable stability for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Under alkaline condition, the overpotentials of OER and HER are 210 mV and 172 mV at a current density of 10 mA cm–2, respectively. Moreover, only a low cell voltage of 1.57 V is required to reach a current density of 10 mA cm–2 in a water splitting device assembled with the Mo-doped NiSe2 as the anode and cathode. Therefore, this study opens up a new way for designing non-precious bifunctional electrocatalysts by Mo doping.

Designing highly-efficient oxygen evolution reaction FeCoNiCrMnOx electrocatalyst via coexisted crystalline and amorphous Phases: Experiment and theory

The design of phase structure was an effective method to improve the catalytic performance of catalysts. In this work, a new electrocatalyst of FeCoNiCrMn based high entropy oxide (HEO) with coexisted crystalline and amorphous phases was designed and analyzed by experimental and theoretical methods. The raising crystallization of specimen could effectively increase the d electron density and d band center of Ni2+ active ion, which contributed to increase the chemical activity of active ion and adjust the catalytic activity of HEO specimen. The designed HEO specimen with coexisted crystalline and amorphous phases exhibited the fairly low experimental oxygen evolution reaction overpotential of 219 mV at the current density of 10 mA cm−2 and 271 mV at the current density 100 mA cm−2 with the small Tafel slope of 42 mV dec-1, fast charge transfer rate, high intrinsic activity TOF of 0.078 s−1 at experimental overpotential of 350 mV and stable electrocatalytic activity, which were better than single crystalline or amorphous phase. This design strategy would be adopted to provide an effective enhancement scheme for HEO systems.