Water Splitting In Acidic Media Research Articles

Multi-Component and Nanoporous Design toward RuO2-Based Electrocatalyst with Enhanced Performance for Acidic Water Splitting.

Developing electrocatalysts with excellent activity and stability for water splitting in acidic media remains a formidable challenge due to the sluggish kinetics and severe dissolution. As a solution, a multi-component doped RuO2 prepared through a process of dealloying-annealing is presented. The resulting multi-doped RuO2 possesses a nanoporous structure, ensuring a high utilization efficiency of Ru. Furthermore, the dopants can regulate the electronic structure, causing electron aggregation around unsaturated Ru sites, which mitigates Ru dissolution and significantly enhances the catalytic stability/activity. The representative catalyst (FeCoNiCrTi-RuO2) shows an overpotential of 167 mV at 10 mAcm-2 for oxygen evolution reaction (OER) in 0.5 m H2SO4 solution with a Tafel slope of 53.1mVdec-1, which is among the highest performance reported. Moreover, it remains stable for over 200 h at a current density of 10mAcm-2. This work presents a promising approach for improving RuO2-based electrocatalysts, offering a crucial advancement for electrochemical water splitting.

Nd–IrO2: High-performance electrocatalyst for enhanced overall water splitting in acidic media

Water electrolysis is one of the most promising green hydrogen production technologies. However, using precious metal materials as electrodes for these electrolyzers incurs high costs. To address these challenges and simultaneously retain the catalytic activity of precious metals, we synthesize a low-iridium catalyst, Nd–IrO2. At 10 and -10 mA/cm2, this catalyst exhibits 233 and 36 mV overpotentials. Nd–IrO2 maintains stability over prolonged operation in acidic environments, as evidenced by its consistent overpotential. Advanced calculations using density functional theory (DFT) have demonstrated that incorporating Nd and an ample amount of oxygen vacancies can modulate the d-band center of Ir and reduce the adsorption energy of electrochemical reaction intermediates. In summary, we present the synthesis of a low-iridium catalyst, which provides valuable insights for the design and development of catalysts with improved electrocatalytic performance.

Partial Exsolution Enables Superior Bifunctionality of Ir@SrIrO3 for Acidic Overall Water Splitting.

The pursuit of efficient and durable bifunctional electrocatalysts for overall water splitting in acidic media is highly desirable, albeit challenging. SrIrO3 based perovskites are electrochemically active for oxygen evolution reaction (OER), however, their inert activities toward hydrogen evolution reaction (HER) severely restrict the practical implementation in overall water splitting. Herein, an Ir@SrIrO3 heterojunction is newly developed by a partial exsolution approach, ensuring strong metal-support interaction for OER and HER. Notably, the Ir@SrIrO3-175 electrocatalyst, prepared by annealing SrIrO3 in 5% H2 atmosphere at 175 °C, delivers ultralow overpotentials of 229 mV at 10 mAcm-2 for OER and 28 mV at 10 mAcm-2 for HER, surpassing most recently reported bifunctional electrocatalysts. Moreover, the water electrolyzer using the Ir@SrIrO3-175 bifunctional electrocatalyst demonstrates the potential application prospect with high electrochemical performance and excellent durability in acidic environment. Theoretical calculations unveil that constructing Ir@SrIrO3 heterojunction regulates interfacial electronic redistribution, ultimately enabling low energy barriers for both OER and HER.

Activity and stability of catalysts for electrocatalytic water splitting in acidic media

Activity and stability of catalysts for electrocatalytic water splitting in acidic media

Efficient Acidic Photoelectrochemical Water Splitting Enabled by Ru Single Atoms Anchored on Hematite Photoanodes.

Photoelectrochemical (PEC) water splitting in acidic media holds promise as an efficient approach to renewable hydrogen production. However, the development of highly active and stable photoanodes under acidic conditions remains a significant challenge. Herein, we demonstrate the remarkable water oxidation performance of Ru single atom decorated hematite (Fe2O3) photoanodes, resulting in a high photocurrent of 1.42 mA cm-2 at 1.23 VRHE under acidic conditions. Comprehensive experimental and theoretical investigations shed light on the mechanisms underlying the superior activity of the Ru-decorated photoanode. The presence of single Ru atoms enhances the separation and transfer of photogenerated carriers, facilitating efficient water oxidation kinetics on the Fe2O3 surface. This is achieved by creating additional energy levels within the Fe2O3 bandgap and optimizing the free adsorption energy of intermediates. These modifications effectively lower the energy barrier of the rate-determining step for water splitting, thereby promoting efficient PEC hydrogen production.

RuO2/CeO2 heterostructure anchored on carbon spheres as a bifunctional electrocatalyst for efficient water splitting in acidic media

The use of proton exchange membrane (PEM) hydrolysis technology holds promise for eco-friendly hydrogen production using renewable energy sources. However, developing efficient, cost-effective, and durable bifunctional electrocatalysts for the acidic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remains challenging. Here, we synthesized RuO2/CeO2 heterojunction loaded on carbon spheres (RuO2/CeO2@C) via hydrothermal and annealing techniques to address this issue. Our experiments demonstrate exceptional catalytic activity of RuO2/CeO2@C for both OER and HER, with overpotentials of 170 and 120 mV, respectively, at 10 mA/cm2 in 0.5 M H2SO4. Moreover, the electrocatalyst enables overall water splitting at 1.54 V and maintains stability for over 100 h at 10 mA/cm2. Density functional theory (DFT) calculations suggest that RuO2/CeO2 heterojunction modifies d-band center of Ru, balances H adsorption/desorption behavior, accelerates reaction kinetics, and lowers the energy barrier, thereby enhancing electrocatalytic activity. These findings provide valuable insights for future efficient bifunctional water splitting electrocatalyst design.

In situ synthesis of self-supported Ir/IrO2 heterostructures via Ar-H2 plasma as efficient bifunctional catalyst for overall water splitting in acidic media

Iridium oxide (IrO2) has been intensively investigated as an efficient and stable anode catalyst for the oxygen evolution reaction (OER) in water splitting system. However, the overall water splitting performance of IrO2 is rarely studied because of its strong adsorption of hydrogen intermediates during the hydrogen evolution reaction (HER) process. Herein, a facile Ar/H2 plasma reduction strategy is developed to activate the HER performance of self-supported IrO2 by constructing a novel metal/oxide heterostructure. The in-situ synthesized Ir/IrO2 composite possesses excellent electrical interconnection and abundant catalytic active sites. Meanwhile, dual active sites induced by the strong interface effect between metallic Ir and IrO2 could optimize the adsorption energy and reaction path for both HER and OER. The optimized Ir–IrO2/Ti@Ar–H2 exhibits remarkable activities with a small overpotential of 58 and 211 mV toward HER and OER, respectively. Besides, Ir–IrO2/Ti@Ar–H2||Ir–IrO2/Ti@Ar–H2 electrolyzer only requires an operational voltage of 1.48 V to afford a current density of 10 mA cm−2, much lower than that of commercial Pt/C||IrO2 (1.61 V).

Synergistic Interface Engineering of RuO2/Co3O4 Heterostructures for Enhanced Overall Water Splitting in Acidic Media

Designing nanocomposites with heterointerface as bifunctional electrocatalysts is a potential strategy to overcome the intrinsic activity limitation of electrocatalytic water splitting in acidic media, but it remains challenging. Herein, the highly efficient RuO2/Co3O4 electrocatalyst with a uniform nanoflower structure is prepared by hydrothermal growth combined with interface engineering. Benefiting from the unique nanostructure, the migration of electrons and intermediates is optimized by the sufficient exposure of abundant micropores and defects. Moreover, the formation of strong electronic interaction at the RuO2/Co3O4 heterointerfaces boosts the electrochemical active surface area and accelerates the reaction kinetics, which effectively improve the catalytic activity and stability of the catalyst. Based on enhanced intrinsic activity and electron transfer, the as‐synthesized RuO2/Co3O4 displays impressive hydrogen evolution reaction and oxygen evolution reaction activity, which respectively require low overpotentials of 240 and 100 mV to achieve a current density of 10 mA cm−2 in 0.5 m H2SO4. As a bifunctional electrode, RuO2/Co3O4 exhibits a low operating voltage of 1.58 V at 10 mA cm−2 for overall electrochemical water splitting. This study demonstrates the importance of heterostructure engineering in providing an avenue to achieve acid‐stable bifunctional electrocatalysts for energy conversion applications.

Two Dimensional Ir-Based Catalysts for Acidic OER.

Electrochemical water splitting in acidic media is one of the most promising hydrogen production technologies, yet its practical applications in proton exchange membrane (PEM) water electrolyzers are limited by the anodic oxygen evolution reaction (OER). Iridium (Ir)-based materials are considered as the state-of-the-art catalysts for acidic OER due to their good stability under harsh acidic conditions. However, their activities still have much room for improvement. Two-dimensional (2D) materials are full of the advantages of high-surface area, unique electrical properties, facile surface modification, and good stability, making the development of 2D Ir-based catalysts more attractive for achieving high catalytic performance. In this review, first, the unique advantages of 2D catalysts for electrocatalysis are reviewed. Thereafter, the classification, synthesis methods, and recent OER achievements of 2D Ir-based materials, including pure metals, alloys, oxides, and perovskites are introduced. Finally, the prospects and challenges of developing 2D Ir-based catalysts for future acidic OER are discussed.

A novel Ir–Ru-based nanoparticle supported on ordered electrochemically synthesized TiO2-nanotube as a highly active and stable oxygen evolution reaction catalyst for water splitting in acidic media

Herein Iridium-Ruthenium-based OER electrocatalysts (Ir: Ru 60:40 at%) supported on electrochemically synthesized TiO2 nanotubes (IrRuOx/TNTs) at 80 wt% have been synthesized by the modified Adams fusion method. Physical and electrochemical characterization of the catalysts is compared with IrRuOx, 80 wt% IrRuOx/TiO2 and commercial RuO2. The total charge and the average diameter of the unsupported IrRuOx are 1655.0 mC mg−1 and 4.98 nm, respectively. The total charge and the average diameter for the IrRuOx/TNT have been obtained at 3647.5 mC mg−1 and 3.77 nm, respectively. IrRuOx/TNT shows a current density of 1000 mA mg−1 at 1.604 VRHE and a Tafel slope of 68.9 mV dec−1. Various methods, such as CV, CP, and CA, have been used to evaluate the stability of the catalysts. The results demonstrate that IrRuOx/TNT is a stable catalyst for use in harsh acidic OER environments and can exhibit good activity in a low noble metal loading.

Insight into the stability mechanism of nickel and manganese antimonate catalytic films during the oxygen evolution reaction in acidic media

Electrochemical water splitting in acidic media is a promising approach for generating hydrogen (H2) gas as a green fuel. In this regard, catalyst design for the oxygen evolution reaction (OER) is more demanding due to the slow transfer kinetics of involved four electrons and high corrosion and degradation of the electrode. Besides, a sustainable OER catalyst should be noble metal-free and have long-term durability under positive potentials in acidic solutions. The current study suggests a nickel-manganese-antimony electrocatalyst synthesized via a facile thermal decomposition method for OER in 0.5 M sulfuric acid. The proposed electrode can generate a current density up to 400 mA cm−2 and withstand 168 h electrolysis under 10 mA cm−2 with an initial overpotential of 598 mV. This stability is largely superior to most of the reported noble metal-free OER catalysts, and the activity has been improved >70 mV compared to the other reported Sb-based electrodes. The 1 week electrochemical stability in acidic media was thoroughly studied by XPS and XRD to analyze the chemical composition and morphology of the electrode before and after the OER, respectively.

High-entropy alloy metallene for highly efficient overall water splitting in acidic media

The preparation of stable and efficient acidic overall water splitting catalysts is crucial to advance the progress of proton exchange membrane water electrolyzers. Herein, we successfully prepared IrPdRhMoW HEA metallene with rich amorphous and crystalline structures. In 0.5 mol L−1 H2SO4, the extraordinary catalytic performance (the overpotentials for hydrogen evolution (HER) and oxygen evolution (OER) of IrPdRhMoW/C at 10 mA cm−2 are 15 mV and 188 mV, respectively) is far stronger than that of commercial catalysts (HER: Pt/C, 47 mV and OER: RuO2, 305 mV) and even other reported noble metal-based catalysts. Using IrPdRhMoW/C for the overall water splitting, only a cell voltage of 1.48 V is required to achieve 10 mA cm−2 and 1.59 V required to achieve 100 mA cm−2, which is the best voltage under high current density reported so far. More importantly, the IrPdRhMoW/C still maintains excellent electroactivity and structural stability after 100 h of water splitting at 100 mA cm−2. Theory calculations reveal the self-balanced effect of electronic structures in the HEA due to the co-existence of crystalline and amorphous lattice structures. The strong orbital couplings not only maximize the electroactivity towards both HER and OER but also stabilize the valence states of metal sites for durable electrocatalysis.

RuO2 nanoparticles anchored on g-C3N4 as an efficient bifunctional electrocatalyst for water splitting in acidic media.

The electrolysis of water, particularly proton exchange membrane (PEM) water electrolysis, holds great promise for hydrogen production in industry. However, the catalyst used in this process is prone to dissolution in acidic environments, making it imperative to develop cost-effective, highly efficient, and acid-stable electrocatalytic materials to overcome this challenge and enable large-scale application of PEM water electrolysis technology. Herein, we prepared ruthenium oxide (RuO2)/graphitic carbon nitride (g-C3N4) composites (RuO2/C3N4) via a combination of sol-gel and annealing methods. The g-C3N4 provides a large surface area, while RuO2 is uniformly deposited on the g-C3N4 surface. The interaction between g-C3N4 and RuO2 stabilizes the RuO2 nanoparticles and enhances long-term water oxidation stability. This unique structure and the combined advantages of RuO2 and g-C3N4 yield exceptional electrocatalytic activity toward both the oxygen evolution reaction (OER, 240 mV@10 mA cm-2) and the hydrogen evolution reaction (HER, 109 mV@10 mA cm-2), with excellent durability (over 28 h), and a cell voltage of 1.607 V at 10 mA cm-2 when used in an RuO2/C3N4||RuO2/C3N4 electrolyzer. This study highlights the efficacy of the g-C3N4 support method in designing highly stable Ru-based OER electrocatalysts for efficient acidic water splitting.

Nanoporous PdIr alloy for high-efficiency and durable water splitting in acidic media

A nanoporous Pd50Ir50alloy is developed for water splitting bifunctional electrocatalysis by metallurgical alloy design and electrochemical dealloying method, outperforming the state-of-the-art catalysts, commercial Pt/C and Ir/C under 0.5 M H2SO4.

Mn-doped Ru/RuO2 nanoclusters@CNT with strong metal-support interaction for efficient water splitting in acidic media

Preparation of low-cost, highly activity and stable bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic media has great challenges. Here, a series of M-Ru/RuO2@CNT (M = Mn, Cd, Cu) bifunctional catalysts were synthesized by doping and strong metal-support interaction (SMSI) strategies to improve the activity and stability of the catalysts. The experiment results show that the optimized Mn–Ru/RuO2@CNT catalyst with ultra-small particle size (2.5 nm) has the best catalytic performance, and the OER and HER tests at 10 mA cm−2 in 0.5 M H2SO4 solution show excellent overpotentials of 177 mV and 30 mV respectively, which are better than most of the catalysts reported recently. In addition, current densities of 10 mA cm−2 and 100 mA cm−2 can be obtained at 1.43 V and 1.51 V when measuring water splitting and can last up to 100 h at a current density of 100 mA cm−2. And this is the first time to achieve the stability of acid water splitting of Ru-based catalyst under large current density. Density functional theory (DFT) calculations show that after manganese doping, the electronic structure is changed by charge redistribution between doped ions and ruthenium-based catalysts containing heterojunctions, and the binding energy of intermediates is optimized to improve the catalytic activity; the stability of the catalyst is improved by increasing the formation energy of ruthenium vacancy and preventing the formation of ruthenium vacancy.

La-RuO2 nanocrystals with efficient electrocatalytic activity for overall water splitting in acidic media: Synergistic effect of La doping and oxygen vacancy

The development of high-performance and durable Ru-based electrocatalysts in proton exchange membrane (PEM) water electrolyzers for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remains a huge challenge due to the severe catalyst’s corrosion and high reaction overpotential in acid media. Herein, we reported a synergistic strategy of effectively combining hetero-atom doping and oxygen vacancy in the La-doped RuO2 nanocrystals, successfully realized by a hydrothermal and followed annealing process aiming for efficiently overall water splitting. The as-obtained La-doped RuO2 nanocrystals demonstrate superior electrocatalytic performances with ultra-low overpotential of 208 mV for OER and 71 mV for HER at the current density of 10 mA/cm2 together with robust long-term stability in 0.5 M H2SO4 electrolyte, which are 222 and 15 mV lower in overpotentials than that of bare RuO2 electrocatalyst. Moreover, the La-doped RuO2 nanocrystals only require a cell voltage of 1.53 V to drive the overall water splitting reaction and exhibit a remarkable stability. Density functional theory (DFT) calculations further reveal that the synergistic effect of La doping and oxygen vacancy engineering could tune the d-band center of Ru active sites and optimize the Gibbs free energy of intermediate state, thus enhancing the activity of RuO2. Such synergistic strategy of aliovalent doping and vacancy engineering for much enhanced acid electrocatalysis may offer important referential values for exploring efficient electrocatalysts towards overall water splitting in acidic media.

Robust interfacial Ru-RuO2 heterostructures for highly efficient and ultrastable oxygen evolution reaction and overall water splitting in acidic media

It is essential but challenging to develop advanced electrocatalysts for oxygen evolution reaction (OER) under acidic conditions to break the activity-stability trade-off. In this work, through the controlled partial oxidation of Ru nanoparticles embedded in amorphous carbon, a robust Ru-RuO2 heterostructure with electronic cooperative interfaces was rationally designed and cleverly constructed. The rich heterogeneous interface between Ru and RuO2 creates a good electronic synergy and achieves high-performance OER electrocatalysis in acidic media. The best Ru-RuO2-NC heterostructure exhibits exceptionally excellent activity with an ultralow overpotential (η10) of 176 mV, a high specific mass activity of 1.37 A mgRu−1 (Jm@1.53 V), and an outstanding long-term durability over 80 h at 10 mA cm−2 in acidic environment. More importantly, the Ru-RuO2-NC heterostructure can further be utilized as a bifunctional electrocatalyst to drive acidic overall water splitting with a low cell voltage of 1.55 V and steady operation for at least 40 h at 10 mA cm2, which possesses potential for implementation in the proton exchange membrane water electrolysis.

Ultrathin IrRu nanocages with tunable electronic reciprocity for highly efficient water splitting in acidic media

Ultrathin IrxRu1−xcubic nanocages with precisely controlled atom accuracy of six atomic layers and well-defined {200} facets exhibit significantly low overpotential for the HER and OER in acidic medium.

Ultrafine ruthenium–iridium–tellurium nanotubes for boosting overall water splitting in acidic media

RuIrTe nanotubes exhibit excellent electrocatalytic activity and stability toward both the hydrogen evolution reaction and oxygen evolution reaction in acidic electrolytes.

Iridium in Tungsten Trioxide Matrix as an Efficient Bi-Functional Electrocatalyst for Overall Water Splitting in Acidic Media.

Electrocatalytic water splitting in acidic media is a promising strategy for grid scale production of hydrogen using renewable energy, but challenges still exist in the development of advanced catalysts with both high activity and stability. Herein, it is reported that iridium doped tungsten trioxide (Ir-doped WO3 ) with arrayed structure and confined Ir sites is an efficient and durable bi-functional catalyst for overall acidic water splitting. A low overpotential (258mV) is required to achieve an oxygen evolution reaction current density of 10mA cm-2 in 0.5 m H2 SO4 solution. Meanwhile, Ir-doped WO3 processes a similar intrinsic activity to Pt/C toward hydrogen evolution reaction. Overall water splitting using the bi-functional Ir-doped WO3 catalyst shows low cell voltages of 1.56 and 1.68V to drive the current densities of 10 and 100mA cm-2 , respectively, with only 16mV decay observed after 60 h continuous electrolysis under the current density of 100mA cm-2 . Structural analysis and density functional theory calculation indicate that the adjusted coordination environment of Ir within the crystalline matrix of WO3 contributes to the high activity and durability.