Electrocatalytic Water Oxidation Activity-Stability Maps for Perovskite Oxides Containing 3d, 4d and 5d Transition Metals

Improving catalytic activity without loss of catalytic stability is one of the core goals in search of low-iridium-content oxygen evolution electrocatalysts under acidic conditions. Here, we synthesize a family of 66 SrBO₃ perovskite oxides (B=Ti, Ru, Ir) with different Ti : Ru : Ir atomic ratios and construct catalytic activity-stability maps over composition variation. The maps classify the multicomponent perovskites into chemical groups with distinct catalytic activity and stability for acidic oxygen evolution reaction, and highlights a chemical region where high catalytic activity and stability are achieved simultaneously at a relatively low iridium level. By quantifying the extent of hybridization of mixed transition metal 3d-4d-5d and oxygen 2p orbitals for multicomponent perovskites, we demonstrate this complex interplay between 3d-4d-5d metals and oxygen atoms in governing the trends in both activity and stability as well as in determining the catalytic mechanism involving lattice oxygen or not.     

HfN Nanoparticles: An Unexplored Catalyst for the Electrocatalytic Oxygen Evolution Reaction

Water electrolysis is one of the most promising methods to produce H₂ and O₂ as high potential fuels. Comparing the two half‐reactions, the oxygen evolution reaction (OER) is the more difficult to be optimized and still relies on expensive noble metal‐based catalysts such as Ru or Ir. In this paper, we prepared nanoparticles of HfN and Hf₂ON₂ and tested them for the OER for the first time. The HfN sample, in particular, showed the highest activity, requiring an overpotential of only 358 mV at 10 mA cm^?2 in Fe‐free electrolyte and, above all, exhibiting long‐term stability. This result places this system amongst one of the most promising catalysts for OER tested to date, in terms of sustainability, activity and stability. The prepared nanoparticles are small (less than 15 nm in diameter), well‐defined in shape and crystalline, and were characterised before and after electrochemical testing also via electron microscopy (EM), powder X‐ray diffraction (PXRD) and X‐ray photoelectron spectroscopy (XPS).     

Activating Inert,Nonprecious Perovskites with Iridium Dopants for Efficient Oxygen Evolution Reaction under Acidic Conditions

Simultaneous realization of improved activity, enhanced stability, and reduced cost remains a desirable yet challenging goal in the search of oxygen evolution electrocatalysts in acid. Herein we report iridium‐containing strontium titanates (Ir‐STO) as active and stable, low‐iridium perovskite electrocatalysts for the oxygen evolution reaction (OER) in acid. The Ir‐STO contains 57 wt % less iridium relative to the benchmark catalyst IrO₂, but it exhibits more than 10 times higher catalytic activity for OER. It is shown to be among the most efficient iridium‐based oxide electrocatalysts for OER in acid. Theoretical results reveal that the incorporation of iridium dopants in the STO matrix activates the intrinsically inert titanium sites, strengthening the surface oxygen adsorption on titanium sites and thereby giving nonprecious titanium catalytic sites that have activities close to or even better than iridium sites.     

Activating Inert,Nonprecious Perovskites with Iridium Dopants for Efficient Oxygen Evolution Reaction under Acidic Conditions

Simultaneous realization of improved activity, enhanced stability, and reduced cost remains a desirable yet challenging goal in the search of oxygen evolution electrocatalysts in acid. Herein we report iridium‐containing strontium titanates (Ir‐STO) as active and stable, low‐iridium perovskite electrocatalysts for the oxygen evolution reaction (OER) in acid. The Ir‐STO contains 57 wt % less iridium relative to the benchmark catalyst IrO₂, but it exhibits more than 10 times higher catalytic activity for OER. It is shown to be among the most efficient iridium‐based oxide electrocatalysts for OER in acid. Theoretical results reveal that the incorporation of iridium dopants in the STO matrix activates the intrinsically inert titanium sites, strengthening the surface oxygen adsorption on titanium sites and thereby giving nonprecious titanium catalytic sites that have activities close to or even better than iridium sites.     

Double Perovskite LaFexNi1−xO3 Nanorods Enable Efficient Oxygen Evolution Electrocatalysis

Perovskite‐based electrocatalysts are one of the most promising materials for oxygen evolution reaction (OER), but their activity and durability are still far from desirable. Herein, we demonstrate that the double perovskite LaFe_xNi_1?xO₃ (LFNO) nanorods (NRs) can be adopted as highly active and stable OER electrocatalysts. The optimized LFNO‐II NRs with Ni/Fe ratio of 8:2 achieve a low overpotential of 302 mV at 10 mA cm^?2 and a small Tafel slope of 50 mV dec^?1, outperforming those of the commercial Ir/C. The LFNO‐II NRs also show high OER stability with slight current decrease after 20 h. The enhanced activity is explained by the improved surface area, tailored electronic structure as well as strong hybridization between O and Ni.     

The Common Intermediates of Oxygen Evolution and Dissolution Reactions during Water Electrolysis on Iridium

Understanding the pathways of catalyst degradation during the oxygen evolution reaction is a cornerstone in the development of efficient and stable electrolyzers, since even for the most promising Ir based anodes the harsh reaction conditions are detrimental. The dissolution mechanism is complex and the correlation to the oxygen evolution reaction itself is still poorly understood. Here, by coupling a scanning flow cell with inductively coupled plasma and online electrochemical mass spectrometers, we monitor the oxygen evolution and degradation products of Ir and Ir oxides in situ. It is shown that at high anodic potentials several dissolution routes become possible, including formation of gaseous IrO₃. On the basis of experimental data, possible pathways are proposed for the oxygen‐evolution‐triggered dissolution of Ir and the role of common intermediates for these reactions is discussed.     

Oxygen Evolution Reaction on Nanoporous Gold Modified with Ir and Pt: Synergistic Electrocatalysis between Structure and Composition

Active oxygen evolution reaction electrocatalysts for water splitting have received great attention because of their importance in the utilization of renewable energy sources. Here, the electrochemical oxygen evolution reaction activities of a nanoporous gold (NPG)‐based electrode in acidic media are investigated. The dependence of the oxygen evolution reaction activity on the NPG surface area shows that the large electrochemical surface areas of the NPG are effectively utilized to enhance electrocatalytic activity. The NPG surfaces are modified with Pt using atomic layer electrodeposition methods, and the resulting NPG@Pt exhibited enhanced electrocatalytic activities compared to those of the NPG and flat Pt electrodes. Ir‐modified NPG (NPG@Ir) electrodes are prepared by spontaneous exchange of Ir on NPG surfaces and exhibit enhanced electrocatalytic activity compared to that of flat Ir surfaces. The modification of NPG@Pt with Ir results in NPG@Pt/Ir electrodes, and their electrocatalytic activities exceed those of NPG@Ir. The enhanced oxygen evolution reaction activity on NPG@Pt/Ir over that on NPG@Ir surfaces is examined by X‐ray photoelectron spectroscopy. The oxygen evolution reaction activity on NPG@Pt/Ir surfaces demonstrates synergistic electrocatalysis between the nanoporous surface structure and active electrocatalytic components.     

Water‐Splitting Electrocatalysis in Acid Conditions Using Ruthenate‐Iridate Pyrochlores

The pyrochlore solid solution (Na_0.33Ce_0.67)₂(Ir_1?xRu_x)₂O₇ (0≤x≤1), containing B‐site Ru^IV and Ir^IV is prepared by hydrothermal synthesis and used as a catalyst layer for electrochemical oxygen evolution from water at pH<7. The materials have atomically mixed Ru and Ir and their nanocrystalline form allows effective fabrication of electrode coatings with improved charge densities over a typical (Ru,Ir)O₂ catalyst. An in situ study of the catalyst layers using XANES spectroscopy at the Ir L_III and Ru K edges shows that both Ru and Ir participate in redox chemistry at oxygen evolution conditions and that Ru is more active than Ir, being oxidized by almost one oxidation state at maximum applied potential, with no evidence for ruthenate or iridate in +6 or higher oxidation states.     

Optimizing the electronic structure of Fe-doped Co3O4 supported Ru catalyst via metal-support interaction boosting oxygen evolution reaction and hydrogen evolution reaction

Metal-support interaction(MSI) is an efficient way in heterogeneous catalysis and electrocatalysis to modulate the electronic structure of metal for enhanced catalytic activity. However, there are still great challenges in promoting the hydrogen evolution reaction(HER) and oxygen evolution reaction(OER) simultaneously by this way. Herein, Fe-doped Co₃O₄ supported Ru(Ru/FeCo) catalysts are synthesized by MSI strategies to further improve the electrocatalytic activity and sta...     

Decorating Pt/C Nanoparticles with Ru by Wall‐Jet Configuration: The Role of Coverage Degree on the Catalyst Activity for Glycerol Electrooxidation

Here, we built Ru‐decorated Pt/C nanoparticles with different coverage degrees (θ_Ru) by wall‐jet configuration for the first time, and we investigated their catalytic properties towards glycerol electrooxidation in acidic medium. Moreover, we used the most active catalysts as the anode in electrolysis to produce carbonyl compounds. The use of an electrochemical cell in wall‐jet configuration allows for the controlling of electrodeposition through easily handling parameters; namely, the θ_Ru is controlled by changing the concentration of the metallic precursor, speed, and volume of injection onto a Pt/C‐modified glassy carbon electrode under applied potential. Excess of Ru on a Pt surface inhibits glycerol dissociative adsorption, which limits further electrooxidation; whereas low θ_Ru do not provide surface oxygen species to the anodic reaction. Hence, intermediates θ_Ru reveal active catalysts – namely, θ_Ru=0.42 shifts the onset potential 170 mV towards lower values and increases 1.65‐fold the current density at 0.5 V. The stability of this catalyst is also enhanced by maintaining a more constant current density during successive potential cycles in the presence of glycerol and by avoiding Ru leaching from the surface. The electrolysis on Ru‐decorated Pt/C is shown to lead the reaction towards formic acid (‘high oxidation state’), decreasing the amounts of glyceradehyde, glycolic acid, and dihydroxyacetone, as a result of the improved catalytic properties.     

碱性介质中碳纳米管FeNi复合物上电催化析氧反应(英文)

Non-noble metals such as Fe and Ni have comparable electrocatalytic activity and stability to that of Ir and Ru in an oxygen evolution reaction (OER). In this study, we synthesized carbon nanofibers with embedded FeNi composites (FeNi-CNFs) as OER electrocatalysts by a facile route comprising electrospinning and the pyrolysis of a mixture of metal precursors and a polymer solution. FeNi-CNFs demonstrated catalytic activity and stability that were better than that of 20 wt% Ir on Vulcan carbon black in oxidizing water to produce oxygen in an alkaline media. Physicochemical and electrochemical characterization revealed that Fe and Ni had synergistic roles that enhanced OER activity by the uniform formation and widening of pores in the carbon structure, while the CNF matrix also contributed to the increased stability of the catalyst.     

Stable Isolated Metal Atoms as Active Sites for Photocatalytic Hydrogen Evolution

The process of using solar energy to split water to produce hydrogen assisted by an inorganic semiconductor is crucial for solving our energy crisis and environmental problems in the future. However, most semiconductor photocatalysts would not exhibit excellent photocatalytic activity without loading suitable co‐catalysts. Generally, the noble metals have been widely applied as co‐catalysts, but always agglomerate during the loading process or photocatalytic reaction. Therefore, the utilization efficiency of the noble co‐catalysts is still very low on a per metal atom basis if no obvious size effect exists, because heterogeneous catalytic reactions occur on the surface active atoms. Here, for the first time, we have synthesized isolated metal atoms (Pt, Pd, Rh, or Ru) stably by anchoring on TiO₂, a model photocatalystic system, by a facile one‐step method. The isolated metal atom based photocatalysts show excellent stability for H₂ evolution and can lead to a 6–13‐fold increase in photocatalytic activity over the metal clusters loaded on TiO₂ by the traditional method. Furthermore, the configurations of isolated atoms as well as the originality of their unusual stability were analyzed by a collaborative work from both experiments and theoretical calculations.     

Channel‐Rich RuCu Nanosheets for pH‐Universal Overall Water Splitting Electrocatalysis

Channel‐rich RuCu snowflake‐like nanosheets (NSs) composed of crystallized Ru and amorphous Cu were used as efficient electrocatalysts for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting in pH‐universal electrolytes. The optimized RuCu NSs/C‐350 °C and RuCu NSs/C‐250 °C show attractive activities of OER and HER with low overpotentials and small Tafel slopes, respectively. When applied to overall water splitting, the optimized RuCu NSs/C can reach 10 mA cm^?2 at cell voltages of only 1.49, 1.55, 1.49 and 1.50 V in 1 m KOH, 0.1 m KOH, 0.5 m H₂SO₄ and 0.05 m H₂SO₄, respectively, much lower than those of commercial Ir/C∥Pt/C. The optimized electrolyzer exhibits superior durability with small potential change after up to 45 h in 1 m KOH, showing a class of efficient functional electrocatalysts for overall water splitting.     

非催化瞬态铱脱溶一筛选铱基钙钛矿析氧催化剂时不可忽视的实验现象

传统化石燃料的过度开采、消耗在推动各国工业化进程的同时,也导致了能源枯竭、环境污染和气候恶化等问题2为应对全球环境治理等难题,推进能源变革,构建脱碳化的能源体系势在必行2质子交换膜电解槽(PEMWE)能够在高电流密度下运行,其体积小,效率高,具有更高的灵活性,更有利于反应进行,能够克服可再生能源(太阳能、风能和水电等)...     

General π‐Electron‐Assisted Strategy for Ir,Pt, Ru,Pd, Fe,Ni Single‐Atom Electrocatalysts with Bifunctional Active Sites for Highly Efficient Water Splitting

Both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are crucial to water splitting, but require alternative active sites. Now, a general π‐electron‐assisted strategy to anchor single‐atom sites (M=Ir, Pt, Ru, Pd, Fe, Ni) on a heterogeneous support is reported. The M atoms can simultaneously anchor on two distinct domains of the hybrid support, four‐fold N/C atoms (M@NC), and centers of Co octahedra (M@Co), which are expected to serve as bifunctional electrocatalysts towards the HER and the OER. The Ir catalyst exhibits the best water‐splitting performance, showing a low applied potential of 1.603 V to achieve 10 mA cm^?2 in 1.0 m KOH solution with cycling over 5 h. DFT calculations indicate that the Ir@Co (Ir) sites can accelerate the OER, while the Ir@NC₃ sites are responsible for the enhanced HER, clarifying the unprecedented performance of this bifunctional catalyst towards full water splitting.     

General π‐Electron‐Assisted Strategy for Ir,Pt, Ru,Pd, Fe,Ni Single‐Atom Electrocatalysts with Bifunctional Active Sites for Highly Efficient Water Splitting

Both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are crucial to water splitting, but require alternative active sites. Now, a general π‐electron‐assisted strategy to anchor single‐atom sites (M=Ir, Pt, Ru, Pd, Fe, Ni) on a heterogeneous support is reported. The M atoms can simultaneously anchor on two distinct domains of the hybrid support, four‐fold N/C atoms (M@NC), and centers of Co octahedra (M@Co), which are expected to serve as bifunctional electrocatalysts towards the HER and the OER. The Ir catalyst exhibits the best water‐splitting performance, showing a low applied potential of 1.603 V to achieve 10 mA cm^?2 in 1.0 m KOH solution with cycling over 5 h. DFT calculations indicate that the Ir@Co (Ir) sites can accelerate the OER, while the Ir@NC₃ sites are responsible for the enhanced HER, clarifying the unprecedented performance of this bifunctional catalyst towards full water splitting.     

Ambient γ-Rays-Mediated Noble-Metal Deposition on Defect-Rich Manganese Oxide for Glycerol-Assisted H2 Evolution at Industrial-Level Current Density

Developing novel synthesis technologies is crucial to expanding bifunctional electrocatalysts for energy-saving hydrogen production. Herein, we report an ambient and controllable γ-ray radiation reduction to synthesize a series of noble metal nanoparticles anchored on defect-rich manganese oxides (M@MnO_2-x, M=Ru, Pt, Pd, Ir) for glycerol-assisted H₂ evolution. Benefiting from the strong penetrability of γ-rays, nanoparticles and defect supports are formed simultaneously and bridged by metal-oxygen bonds, guaranteeing structural stability and active site exposure. The special Ru−O−Mn bonds activate the Ru and Mn sites in Ru@MnO_2-x through strong interfacial coordination, driving glycerol electrolysis at low overpotential. Furthermore, only a low cell voltage of 1.68 V is required to achieve 0.5 A cm⁻² in a continuous-flow electrolyzer system along with excellent stability. In situ spectroscopic analysis reveals that the strong interfacial coordination in Ru@MnO_2-x balances the competitive adsorption of glycerol and OH* on the catalyst surface. Theoretical calculations further demonstrate that the defect-rich MnO₂ support promotes the dissociation of H₂O, while the defect-regulated Ru sites promote deprotonation and hydrogen desorption, synergistically enhancing glycerol-assisted hydrogen production.     

Low‐Coordinate Iridium Oxide Confined on Graphitic Carbon Nitride for Highly Efficient Oxygen Evolution

Highly active and durable electrocatalysts for the oxygen evolution reaction (OER) is greatly desired. Iridium oxide/graphitic carbon nitride (IrO₂/GCN) heterostructures are designed with low‐coordinate IrO₂ nanoparticles (NPs) confined on superhydrophilic highly stable GCN nanosheets for efficient acidic OER. The GCN nanosheets not only ensure the homogeneous distribution and confinement of IrO₂ NPs but also endows the heterostructured catalyst system with a superhydrophilic surface, which can maximize the exposure of active sites and promotes mass diffusion. The coordination number of Ir atoms is decreased owing to the strong interaction between IrO₂ and GCN, leading to lattice strain and increment of electron density around Ir sites and hence modulating the attachment between the catalyst and reaction intermediates. The optimized IrO₂/GCN heterostructure delivers not only by far the highest mass activity among the reported IrO₂‐based catalysts but also decent durability.     

Three‐Dimensional Branched and Faceted Gold–Ruthenium Nanoparticles: Using Nanostructure to Improve Stability in Oxygen Evolution Electrocatalysis

Achieving stability with highly active Ru nanoparticles for electrocatalysis is a major challenge for the oxygen evolution reaction. As improved stability of Ru catalysts has been shown for bulk surfaces with low‐index facets, there is an opportunity to incorporate these stable facets into Ru nanoparticles. Now, a new solution synthesis is presented in which hexagonal close‐packed structured Ru is grown on Au to form nanoparticles with 3D branches. Exposing low‐index facets on these 3D branches creates stable reaction kinetics to achieve high activity and the highest stability observed for Ru nanoparticle oxygen evolution reaction catalysts. These design principles provide a synthetic strategy to achieve stable and active electrocatalysts.     

A Dissolution/Precipitation Equilibrium on the Surface of Iridium‐Based Perovskites Controls Their Activity as Oxygen Evolution Reaction Catalysts in Acidic Media

Recently, Ir^V‐based perovskite‐like materials were proposed as oxygen evolution reaction (OER) catalysts in acidic media with promising performance. However, iridium dissolution and surface reconstruction were observed, questioning the real active sites on the surface of these catalysts. In this work, Sr₂MIr^(V)O₆ (M=Fe, Co) and Sr₂Fe_0.5Ir_0.5^(V)O₄ were explored as OER catalysts in acidic media. Their activities were observed to be roughly equal to those previously reported for La₂LiIrO₆ or Ba₂PrIrO₆. Coupling electrochemical measurements with iridium dissolution studies under chemical or electrochemical conditions, we show that the deposition of an IrO_x layer on the surface of these perovskites is responsible for their OER activity. Furthermore, we experimentally reconstruct the iridium Pourbaix diagram, which will help guide future research in controlling the dissolution/precipitation equilibrium of iridium species for the design of better Ir‐based OER catalysts.