pH-universal Electrocatalysts Research Articles

Defect-rich CoRu alloy embedded in the porous carbon serving as highly-efficient and bifunctional electrocatalyst for overall water splitting over a wide pH range

Exploring highly-efficient and pH-universal overall water splitting electrocatalysts are critical but keep challenging. Herein, a highly-efficient, dual-function and pH-universal electrocatalyst consisting of CoRu alloy nanoparticles embedded in the carbon matrix (CoRu/C) was successfully synthesized through an acid etching-pyrolysis conversion process using ZIF-67 as a precursor. Benefiting from the rich crystal defects created during the alloy formation process that could serve as active catalytic sites and the optimized electronic structure, the as-obtained CoRu/C electrocatalyst required overpotentials of only 18 and 37 mV to reach a current density of 10 mA cm−2 for hydrogen evolution reaction (HER) and 184 and 170 mV for oxygen evolution reaction (OER) in 1.0 M KOH and 0.5 M H2SO4 aqueous solution, respectively. For practical application, the CoRu/C catalyst only needs a cell voltage of 1.49 and 1.45 V in a two-electrode overall water splitting system to achieve a current density of 10 mA cm−2 in alkaline and acidic medium, respectively. The present work paves a new way for the design and construction of efficient bifunctional electrocatalyst for overall water splitting, and would inspire widespread research interest in the field of energy storage and conversion.

Wrinkled Ir-MnOx nanospheres as pH-universal electrocatalysts for oxygen evolution reaction

Wrinkled Ir-doped manganese oxide (Ir-MnOx) nanospheres have been prepared via a facile metal–organic framework-directed strategy as pH-universal OER electrocatalysts.

Constructing Fe–N-doped porous carbon nanofibers for a pH-universal ORR and switchable, superior Zn–air batteries

Efficient pH-universal electrocatalysts composed of highly dispersive tiny Fe nanoparticle units in a carbon nanofiber network is reported. The as-assembled zinc–air batteries in alkaline and neutral electrolytes exhibit excellent overall performance.

Metallic Mo, Ru coupled with graphitic carbon dots to activate inertness 1D copper-based nanowires as efficient electrocatalyst for pH-universal hydrogen evolution reaction

Designing efficient and robust pH-universal electrocatalysts for hydrogen evolution reaction (HER) is the key to boost the development of eco-friendly hydrogen energy. Herein, metallic Mo, Ru coupled with graphitic carbon dots (GQDs) activate inertness 1D copper-based nanowires (GQDs@ Ru, Mo-Cu2O/CF) by surface chemical oxidation, solvothermal and low temperature calcination. The metals of Mo, Ru favor the water-dissociation and optimize the hydrogen adsorption/desorption. In addition, GQDs owns edge effect and good conductivity, and then benefiting electron transport and active sites exposure. Therefore, the synthesized GQDs@ Ru, Mo-Cu2O/CF requires only 30, 39, 17 and 55 mV in alkaline, acidic, alkaline seawater and neutral to achieve 10 mA cm−2. Moreover, the assembled electrolyzer requires 1.58 V to reach 10 mA cm−2 in alkaline seawater, and maintained well at 200 mA cm−2 for 100 h. This research opens a new avenue for designing efficient catalysts on energy-relation applications through introducing both metal and non-metal.

Interface regulation of Zr-MOF/Ni2P@nickel foam as high-efficient electrocatalyst for pH-universal hydrogen evolution reaction

Currently, the development of economical and effective non-noble metal electrocatalysts is vital for advancing hydrogen evolution reaction (HER) and enabling its widespread applications. The customizable pore structure and enormous surface area of metal–organic frameworks (MOFs) have made them to become promising non-noble metal electrocatalysts for HER. However, MOFs have some challenges, including low conductivity and instability, which can result in them having high overpotentials and slow reaction kinetics in electrocatalytic processes. In this work, we present an innovative approach for synthesizing cost-effective and high-efficient Zr-MOF-derived pH-universal electrocatalysts for HER. It entails creating the interfaces of the electrocatalysts with suitable proportions of phosphide nanostructures. Zr-MOF/Ni2P@nickel foam (NF) electrodes with interface regulated by Ni2P nanostructures were successfully developed for high-efficient pH-universal HER electrocatalysts. The presence of Ni2P nanostructures with abundant active sites at the Zr-MOFs@NF interfaces boosted the electronic conductivity and local charge density of the hybrid electrocatalysts. This helped to improve their reaction kinetics and electrocatalytic activity. By optimizing the Ni2P amount, Zr-MOF/Ni2P@NF demonstrated impressive stability and superior HER activities, with a low overpotential of 149 mV (acidic electrolytes) and 143 mV (alkaline electrolytes) at 10 mA cm−2. The proven strategy in this work can be expanded to many types of MOF-based materials for wider practical applications.

Interfacial synergistic effect of Ru nanoparticles embedded onto amorphous/crystalline WO3 nanorods on boosting the pH-universal hydrogen evolution reaction

The development of high-efficiency pH-universal electrocatalyst is of great significance for hydrogen evolution reaction (HER). In this work, a rod-like Ru/WO3-VO electrocatalyst was constructed for HER via a solid-phase reaction strategy. Due to the restriction of atomic migration at solid phase interface, plenty of oxygen vacancies (VO) and structure distortions were generated in amorphous/crystalline WO3 phase (WO3-VO). The optimized Ru/WO3-VO annealed at 450 °C with 2.2 wt% Ru achieves outstanding intrinsic activity with low overpotential and Tafel slope in a 0–14 pH range. A turnover frequency value 7.2 higher than that of commercial Pt/C is abtaind on Ru/WO3-VO at overpotential of 100 mV. Density functional theory calculations reveal that H* adsorption and desorption balanced by tuning the interface electronic structure contributes synergistic effect to the pH-universal HER activity of Ru/WO3-VO. The crystalline/amorphous semiconductor-metal heterointerface is crucial to designing and synthesizing electrocatalysts for optimal HER activity.

Conjugated Nickel Phthalocyanine Derivatives for Heterogeneous Electrocatalytic H2 O2 Synthesis.

Electrocatalytic hydrogen peroxide (H2 O2 ) production has emerged as a promising alternative to the chemical method currently used in industry, due to its environmentally friendly conditions and potential for higher activity and selectivity. Heterogeneous molecular catalysts are promising in this regard, as their active site configurations can be judiciously designed, modified, and tailored with diverse functional groups, thereby tuning the activity and selectivity of the active sites. In this work, nickel phthalocyanine derivatives with various conjugation degrees are synthesized and identified as effective pH-universal electrocatalysts for H2 O2 production after heterogenized on nitrogen-decorated carbon, with increased conjugation degrees leading to boosted selectivity. This is explained by the regulated d-band center, which optimized the binding energy of the reaction intermediate, reducing the energy barrier for oxygen reduction and leading to optimized H2 O2 selectivity. The best catalyst, NiPyCN/CN, exhibits a high H2 O2 electrosynthesis activity with ≈95% of H2 O2 faradic efficiency in an alkaline medium, demonstrating its potential for H2 O2 production.

Facile synthesis of hierarchically ordered Mo2C/Co3Mo3C@C nanosheet heterostructure: A highly durable pH universal electrocatalyst for hydrogen evolution reaction and overall alkaline water splitting

Developing cost-effective, high-efficiency, earth-abundant electrode materials for hydrogen evolution reaction (HER) operating in wide pH range electrolytes is significant for large-scale hydrogen generation. However, the rational design of highly stable electrocatalysts with robust performance remains challenging. Herein, in-situ construction of hierarchically ordered Mo2C/Co3Mo3C nanosheet heterostructure (CMC/MC@C) is achieved by the simple pyrolysis method. The optimized Co1Mo1C/550 catalyst achieves a low HER overpotential of 86, 102, and 323 mV at 10 mA cm−2 current density in 1.0 M KOH, 0.5 M H2SO4, and 0.1 M PBS solutions, respectively, with robust durability over 48 h. Benefiting from the bifunctionality of Co1Mo1C/550, the electrocatalyst achieves a current density of 10 mA cm−2 at a low overpotential of 336 mV towards the oxygen evolution reaction (OER) and 1.597 V for overall water splitting in a 1.0 M KOH solution. The exceptional performance of the as-prepared catalyst is primarily attributable to the strong synergistic relationship between Co3Mo3C and Mo2C particles, hierarchically ordered porous carbon nanosheet structure, and superhydrophilic electrode surface, which not only provide rich exposed active sites but also boost the access of electrolytes and the diffusion of H2 bubbles, thereby effectively enhancing the HER and OER performances. This study offers a new approach to the rational design of various transition metal-based carbide electrode materials via the structural optimization strategy for reliable and efficient universal pH catalysts towards HER and overall alkaline water splitting.

Ru-doped MoO2/Mo2C coupled with N-doped carbon as an efficient pH-universal electrocatalyst for hydrogen generation

The preparation of stable, efficient and pH-universal hydrogen evolution reaction (HER) electrocatalysts is urgent and significant for large-scale hydrogen production. Herein, a simple and efficient method was developed to fabricate Ru-doped MoO2/Mo2C onto N-doped carbon nanoparticles (Ru-MoO2/Mo2C/NC). The formed smaller nanoparticles by Ru doping can provide abundant accessible active sites and interfaces. Moreover, the synergistic effects of Ru and Mo-based compounds also played a key role in promoting the catalytic kinetics. The as-prepared Ru-MoO2/Mo2C/NC exhibited low overpotentials of 38, 61, 67 and 75 mV in alkaline, neutral, acidic electrolyte solutions and alkaline seawater at 10 mA cm−2, respectively. This work proposes a valid method for the design of efficient electrocatalysts through precise component regulation.

Construction of urchin-like bimetallic phosphides induced by carbon dots for efficient wide pH hydrogen production

The development of an efficient noble-metal-free and pH-universal electrocatalyst for the hydrogen evolution reaction (HER) would be highly significant for hydrogen (H2) production via electrocatalytic water splitting. However, developing such a catalyst remains a formidable task. Herein, a strategy is proposed for the in situ fabrication of a novel urchin-like NiCoP microsphere catalyst (0.5CDs-NiCoP/NF) on nickel foam (NF) using carbon dots (CDs) as a directing agent. The strong bonding between the CDs and metals provides additional active sites, giving 0.5CDs-NiCoP/NF excellent electrocatalytic hydrogen evolution performance in environments ranging from acidic to basic. Moreover, the unique structure of 0.5CDs-NiCoP/NF endows this catalyst with low Tafel slopes of 73, 146 and 74 mV dec−1 for HER in acidic, neutral and alkaline conditions, respectively. This performance exceeds that of numerous other reported non-precious HER catalysts. In summary, this work offers a novel and efficient strategy for the design and synthesis of low-cost, efficient, and robust transition metal phosphides (TMPs) electrocatalysts.

Phase transition engineering of nanoporous pyrite-phase NiSe2 foam by phosphorus doping for robust pH-universal hydrogen evolution

The present non-precious hydrogen-evolving electrocatalysts deliver high catalytic activity either in acidic or basic media but very few simultaneously exhibit superb catalytic efficiency and stability for hydrogen evolution reaction (HER) in a wide pH range, especially for pyrite-phase materials (e.g., CoS2, NiSe2), probably due to their high kinetic energy barriers of initial water dissociation process. Herein, we report a phase transition engineering of pyrite-phase porous NiSe2 into NiP1.86Se0.14 by heavy phosphorus doping, which performs excellently as a pH-universal electrocatalyst for HER. In this material, P atom replaces the sub-selenium atom in NiSe2 to modulate the electronic structures and spin states of Ni sites with lower d-band center, thus promoting sluggish hydrogen adsorption, water adsorption, and dissociation dynamics. As a result, this catalyst exhibits superior hydrogen-evolving catalytic activity in multiple media in terms of relatively low overpotentials of 56.8 and 79 mV at a current density of 10 mA cm−2 in 0.5 M H2SO4 and 1.0 M KOH, respectively. Particularly, this porous NiP1.86Se0.14 shows good stability toward hydrogen evolution in both acidic and alkaline media, with little variation in potentials after continuous operation for approximately 80 and 70 h at 30 mA cm−2. This work may provide a promising solution to address the poor catalytic HER activity and instability of transition metal selenides under alkaline conditions.

Hierarchical SiC-Graphene Composite Aerogel-Supported Ni-Mo-S Nanosheets for Efficient pH-Universal Electrocatalytic Hydrogen Evolution.

MoS2 exhibits good prospects in electrocatalytic hydrogen evolution. Whereas, the electrocatalytic property of MoS2 is restrained by its insufficient active sites, low electrical conductivity, and slow water dissociation processes. Herein, an aerogel composed of silicon carbide (SiC) and graphene (SiCnw-RGO) was constructed by growing SiC nanowires (SiCnw) in the graphene aerogel (RGO) via the CVD method, and then Ni-Mo-S nanosheets were hydrothermally synthesized on the SiCnw-RGO composite aerogel to develop an efficient pH-universal electrocatalyst. Ni-Mo-S nanosheets supported on SiCnw-RGO (Ni-Mo-S@SiCnw-RGO) exhibit an interesting hierarchical three-dimensional interconnected structure of composite aerogel. The optimal Ni-Mo-S@SiCnw-RGO electrocatalyst exhibits excellent catalytic performance with low Tafel slopes of 60 mV/dec under acidic conditions and 90 mV/dec under alkaline conditions. Density functional theory calculations demonstrate a composite catalyst exhibits advantageous hydrogen adsorption free energy and water dissociation energy barrier. This study provides a reference to design an efficient hierarchical aerogel electrocatalyst.

Janus Ru/RuO2 nano-boomerangs on carbon as pH-universal electrocatalysts with bifunctional activity toward the hydrogen/oxygen evolution reaction

Efficient pH-universal overall water-splitting electrocatalysts are critical for reducing energy consumption and simplifying cell design; however, challenges remain. In this study, we report a scalable method for the preparation of new carbon-supported Ru/RuO2 nano-boomerangs (Ru/RuO2NB/C). The Ru/RuO2NB with a novel Janus nanostructure exposes both Ru and RuO2 active sites independently on the two arms of the nano-boomerangs without inhibiting their activities. Herein, for the first time, it is demonstrated that carbon promotes the reduction of RuO2 to Ru at relatively low temperatures (∼300 °C) without any other reductants. A new facile process was developed for the preparation of well-dispersed RuO2 nanorods on carbon supports (RuO2NR/C), which were then converted to a Ru/RuO2NB Janus nanostructure. The synthesized Ru/RuO2NB/C exhibits excellent bifunctional catalytic activity and robust stability toward the hydrogen/oxygen evolution reaction (HER/OER) in an aqueous solution over the whole pH range. The OER/HER metal mass activity (jm)/turnover frequency (TOF) of Ru/RuO2NB/C is five times higher than that of commercial RuO2/C in acidic, neutral, or alkaline aqueous solutions. In a wide pH range, the TOF and jm of Ru/RuO2NB/C are higher than those of most OER and HER electrocatalysts. The HER activity of Ru/RuO2NB/C surpassed that of Pt/C in an alkaline solution. The tannic acid (TA) fragment from TA modification of carbon produces the high thermal stability of Ru/RuO2NB/C catalysts.

Understanding the copper-iridium nanocrystals as highly effective bifunctional pH-universal electrocatalysts for water splitting

It is pivotal to develop an economical, effective, and stable catalyst to promote the oxygen/hydrogen evolution reaction (OER/HER) throughout pH electrolytes, as the demand for hydrogen energy will increase greatly with the future development. Herein, a series of Ir-Cu nanoparticle composite carbon (IrxCuy/C) catalysts are successfully synthesized using ethylene glycol reduction. In addition, the structure, morphology and composition of the electrocatalysts were systematically characterized, and the OER/HER performance of the catalysts was also tested under different pH conditions. According to experimental findings, amorphous Ir3Cu/C has superior competent performance to catalyze oxygen (O2) production in alkaline and acidic environments. The comparatively low overpotentials required are 222 mV and 304 mV, respectively, while generating a current density of 10 mA cm−2. The reduced amount of precious metal and the further improvement in activity and durability make Ir3Cu/C an excellent noble metal-based electrocatalyst. Meanwhile, IrCu/C has significant electrocatalytic performance for the HER in acidic media.

High-Activity Fe3 C as pH-Universal Electrocatalyst for Boosting Oxygen Reduction Reaction and Zinc-Air Battery.

Transition metal catalysts are regarded as one of promising alternatives to replace traditional Pt-based catalysts for oxygen reduction reaction (ORR). In this work, an efficient ORR catalyst is synthesized by confining Fe3 C nanoparticles into N, S co-doped porous carbon nanosheets (Fe3 C/N,S-CNS) via high-temperature pyrolysis, in which 5-sulfosalicylic acid (SSA) demonstrates as an ideal complexing agent for iron (ΙΙΙ) acetylacetonate while g-C3 N4 behaves as a nitrogen source. The influence of the pyrolysis temperature on the ORR performance is strictly examined in the controlled experiments. The obtained catalyst exhibits excellent ORR performance (E1/2 = 0.86V; Eonset = 0.98V) in alkaline electrolyte, coupled by exhibiting the superior catalytic activity and stability (E1/2 = 0.83V, Eonset = 0.95V) to Pt/C in acidic media. In parallel, its ORR mechanism is carefully illustrated by the density functional theory (DFT) calculations, especially the role of the incorporated Fe3 C played in the catalytic process. The catalyst-assembled Zn-air battery also exhibits a much higher power density (163mW cm-2 ) and ultralong cyclic stability in the charge-discharge test for 750h with a gap increase down to 20mV. This study provides some constructive insights for preparation of advanced ORR catalysts in green energy conversion units correlated systems.

Ultra-fine Ru nanoparticles decorated V2O3 as a pH-universal electrocatalyst for efficient hydrogen evolution reaction

Developing high-efficiency electrocatalysts viable for pH-universal hydrogen evolution reaction (HER) has attracted great interest because hydrogen is a promising renewable energy carrier for replacing fossil fuels. Herein, we present a facile strategy for fabricating ultra-fine Ru nanoparticles (NPs) decorated V2O3 on the carbon cloth substrates as efficient and stable pH-universal catalysts for HER. Benefiting from the metallic property and electronic conductivity of V2O3 matrix, the optimized hybrid (Ru/V2O3-CC) exhibits excellent HER activities in a wide pH range, achieving lower overpotentials of 184, 219, and 221 mV at 100 mA cm−2 in 0.5 M H2SO4, 1.0 M KOH and 1.0 M phosphate-buffered saline, respectively. Moreover, the electrode remains superior stability with negligible degradation after 5000 cyclic voltammetry scanning whether in acidic, alkaline or neutral media. Experimental results, combined with theoretical calculations, demonstrate that the interaction between Ru NPs and the support V2O3 induces the local electronic density diversity, allowing optimization of the adsorption energy of Ru towards hydrogen intermediate H∗, thus favoring the HER process.

Silver-decorated cobalt–molybdenum oxide nanosheets as a pH-universal electrocatalyst for high-efficiency hydrogen evolution reaction

The high efficiency of hydrogen evolution reaction (HER) catalysts depends on their electronic structure, conductivity, and intrinsic catalytic activity. Transition-metal oxides (TMO) present a great potential to replace platinum-based catalysts, but further improvements in intrinsic catalytic activity are limited to the materials' conductivity. Herein, theoretical calculations disclosed that the adjusted density of states around the Fermi level caused by Ag introduction increased the conductivity of Co2Mo3O8-Ag, optimizing the water adsorption energy (ΔEad) and Gibbs free energy of hydrogen adsorption (ΔGH*). This can be rationalized through the synergistic effect between electron-rich Co and Mo sites in Co2Mo3O8-Ag. Inspired by this, Ag nanoparticles loaded on Co2Mo3O8 nanosheets (CMO-Ag) as a pH-universal HER catalyst were successfully constructed. As expected, the prepared CMO-Ag catalyst exhibited excellent HER activity with overpotentials of 55.5, 63.2, and 68.2 mV at a current density of 10 mA cm−2 in alkaline, neutral, and acidic electrolyte, respectively, superior to most reported results from molybdenum/cobalt-based electrocatalyst. Meanwhile, the CMO-Ag also presented exceptional stability with negligible change after 20 h of stability tests and 1000 cycles of CV measurements. This work provides a valuable strategy for optimizing catalytic activity sites and improving conductivity through combining metal nanoparticles and TMO, which can be applied for other TMO-based HER pH-universal catalyst.

Fabrication of CoS2-MoS2 heterostructure via interface engineering toward efficient dual-pH hydrogen evolution

Modulation of electronic structure via heterointerface engineering is regarded as an appealing strategy to promote the hydrogen evolution reaction (HER) performance of a pH-universal electrocatalyst. Herein, the CoS2-MoS2 heterostructure is synthesized, where MoS2 nanosheets are vertically anchored on CoS2 microflakes. Plentiful heterogeneous nanointerfaces generated between MoS2 and CoS2 phases not only provide sufficient electroactive sites and structural defects, but also afford a hierarchically porous structure. The synergistic modulation of electronic and geometric structures accounts for a superb catalytic activity and long-durability of CoS2-MoS2 toward HER in acidic and alkaline solutions simultaneously, in terms of the overpotential in 0.5 M H2SO4 (218 mV versus RHE) and 1.0 M KOH (251 mV) at a current density of 10 mA cm−2. This work offers an exciting avenue for fabricating transition metal sulfides as efficient wide-pH electrocatalysts through an interface-induced strategy.

The Promotional Effect of Na on Ru for pH-Universal Hydrogen Evolution Reactions

Alkali metals, as ideal electron donors, can effectively regulate the valence state distribution of the host metals. Nevertheless, no studies have reported the application of alkali metal promoters in the hydrogen evolution reaction (HER). Here, we designed an efficient and wide pH-universal hydrogen evolution catalyst that utilizes alkali metal to control the valence, size, and dispersion of Ru NPs. The experimental results reveal that the alkali metal additives contribute to the dispersion and stabilization of metallic Ru. More importantly, the interaction between Na and Ru regulates the distribution of Ru valence states and helps to form more active components of Ru0. Additionally, NaCl functioned as an in situ template to assist the construction of a porous carbon skeleton promotes mass transfer and exposes more active sites, further promoting the synergistic effect of Ru and Na. As a result, the optimal Ru0.3/C−800 delivers high efficiency for HER with an overpotential as low as 29 mV in 1.0 M KOH and 83 mV in 0.5 M H2SO4 under 10 mA cm−2. Particularly, the catalytic performance of Ru0.3/C−800 even outbalanced that of commercial Pt/C in an alkaline medium. This rational construction strategy opens up new avenues for obtaining superior pH-universal electrocatalysts.

Encapsulating dual-phase WC-W2C nanoparticles into hollow carbon dodecahedrons for all-pH electrocatalytic hydrogen evolution

Designing robust and reliable pH-universal electrocatalyst for H2 production is highly desirable for industrial water splitting, but still remains great challenge. Herein, dual-phase WC-W2C nanocrystals embedded into hollow carbon dodecahedrons (denoted as WC-W2C/HCDs) is obtained via a template-engaged method. Combining hollow structure and befitting phase compositions, dual-phase WC-W2C/HCDs exhibits competitive HER activities, requiring only 96, 148 and 116 mV overpotentials to drive 10 mA cm−2 in 0.5 M H2SO4, 1.0 M phosphate-buffered saline (PBS), and 1.0 M KOH, respectively, which displays superior activity toward the HER to the single-phase WC/HCDs and W2C/HCDs. Meanwhile, it also exhibits an exceptionally durability in 0.5 M H2SO4 acid electrolyte, showing insignificant degradation over 150 h of H2 production, as well as durable in neutral and alkaline conditions. Such excellent HER ability is benefit from the heterointerfaces between WC and W2C that yield the strong electronic coupling interactions, providing beneficial sites for both intermediate H* adsorption energy and water dissociation. Moreover, the hollow carbon dodecahedrons exhibit overall enhancement in electrical conductivity, exposure of catalytic active sites, long-term durability in wide range of pH (0–14). This strategy may open up a new possibility for the rational design of dual-phase carbide and others electrocatalysts toward pH-universal H2 production.