Amorphization activated ruthenium-tellurium nanorods for efficient water splitting

Defective PtRuTe As Nanozyme with Selectively Enhanced Peroxidase-like Activity

Noble metal based nanozymes show great potential in replacing natural enzymes; however, their development is greatly restricted by their relatively low specificity and activity. Herein, we report the synthesis of a class of amorphous/crystalline PtRuTe nanomaterials with a Pt/Te-enriched core and a Ru-enriched shell as efficient peroxidase mimics with selectively enhanced peroxidase-like activity and suppressed oxidase-like activity. We demonstrate that amorphous domains play a critical role in tuning and optimizing the catalytic properties. The PtRuTe nanozyme with high-percentage defects exhibits superior catalytic activities and kinetics, and the suppressed oxidase-like activity could diminish the interference of O2 in the glucose colorimetric assay. The high catalytic performance can be caused by amorphous phase induced electron redistribution and electronic interactions between different elements and the synergistic effect of multimetallic nanocrystals. The concurrent extraordinary peroxidase-like activity and suppressed oxidase-like activity guarantee the amorphous/crystalline PtRuTe nanozymes as promising alternatives of natural enzymes for biosensing and beyond.

Engineering Amorphous/Crystalline Rod-like Core-Shell Electrocatalysts for Overall Water Splitting

The design of bifunctional electrocatalysts for hydrogen and oxygen evolution reactions delivering excellent catalytic activity and stability is highly desirable, yet challenged. Herein, we report an amorphous RuO₂-encapsulated crystalline Ni_0.85Se nanorod structure (termed as a/c-RuO₂/Ni_0.85Se) for enhanced HER and OER activities. The as-prepared a/c-RuO₂/Ni_0.85Se nanorods not only demonstrate splendid HER activity (58 mV@10 mA cm^-2 vs RHE), OER activity (233 mV@10 mA cm^-2 vs RHE), and electrolyzer activity (1.488 V@10 mA cm^-2 vs RHE for overall water splitting) but also exhibit long-term stability with negligible performance decay after 50 h continuous test for overall water splitting. In addition, the variation of the d-band center (from the perspective of bonding and antibonding states) is unveiled theoretically by density functional theory calculations upon amorphous RuO₂ layers coupling to clarify the increased hydrogen species adsorption for HER activity enhancement. This work represents a new pathway for the fabrication of bifunctional electrocatalysts toward green hydrogen generation.

Sequential galvanic replacement mediated Pd-doped hollow Ru-Te nanorods for enhanced hydrogen evolution reaction mass activity in alkaline media

High catalytic activity, long-term stability, and economical Pt-free catalysts for the hydrogen evolution reaction (HER) are required for the conversion of renewable energy systems. Noble nanomaterial Pt is a superior electrolysis catalyst for water splitting under typical experimental conditions with a relatively low overpotential. However, the use of Pt is limited by its high cost and activity degradation over time. Among several prospective alternatives, Ru has emerged as a promising alkaline electrolysis catalyst because of its significant catalytic activity and reduced cost compared to Pt. We designed and suggested Pd-doped hollow Ru-Te nanorods (PdRuTeNRs) via successive galvanic replacement reactions of sacrificial Te nanotemplates to further boost efficiency. The Pd/partially oxidized RuO₂/Ru/Te hetero-interfaced composition exhibited an HER mass activity of 11.3 A g^-1 Ru, twice that of Pt. In addition, the present PdRuTeNRs sufficiently maintained the activity from the 2000-cycle continuous test, greatly reducing the required cost by a quarter.

Reconstruction of Highly Dense Cu−N 4 Active Sites in Electrocatalytic Oxygen Reduction Characterized by Operando Synchrotron Radiation

The emerging star of single atomic site (SAS) catalyst has been regarded as the most promising Pt-substituted electrocatalyst for oxygen reduction reaction (ORR) in anion-exchange membrane fuel cells (AEMFCs). However, the metal loading in SAS directly affects the whole device performance. Herein, we report a dual nitrogen source coordinated strategy to realize high dense Cu-N₄ SAS with a metal loading of 5.61 wt% supported on 3D N-doped carbon nanotubes/graphene structure wherein simultaneously performs superior ORR activity and stability in alkaline media. When applied in H₂ /O₂ AEMFC, it could reach an open-circuit voltage of 0.90 V and a peak power density of 324 mW cm^-2 . Operando synchrotron radiation analyses identify the reconstruction from initial Cu-N₄ to Cu-N₄ /Cu-nanoclusters (NC) and the subsequent Cu-N₃ /Cu-NC under working conditions, which gradually regulate the d-band center of central metal and balance the Gibbs free energy of *OOH and *O intermediates, benefiting to ORR activity.

Coupling of nanocrystal hexagonal array and two-dimensional metastable substrate boosts H2-production

Designing well-ordered nanocrystal arrays with subnanometre distances can provide promising materials for future nanoscale applications. However, the fabrication of aligned arrays with controllable accuracy in the subnanometre range with conventional lithography, template or self-assembly strategies faces many challenges. Here, we report a two-dimensional layered metastable oxide, trigonal phase rhodium oxide (space group, P-3m1 (164)), which provides a platform from which to construct well-ordered face-centred cubic rhodium nanocrystal arrays in a hexagonal pattern with an intersurface distance of only 0.5 nm. The coupling of the well-ordered rhodium array and metastable substrate in this catalyst triggers and improves hydrogen spillover, enhancing the acidic hydrogen evolution for H2 production, which is essential for various clean energy-related devices. The catalyst achieves a low overpotential of only 9.8 mV at a current density of -10 mA cm-2, a low Tafel slope of 24.0 mV dec-1, and high stability under a high potential (vs. RHE) of -0.4 V (current density of ~750 mA cm-2). This work highlights the important role of metastable materials in the design of advanced materials to achieve high-performance catalysis.

Catalysis of Alloys: Classification, Principles, and Design for a Variety of Materials and Reactions

Alloying has long been used as a promising methodology to improve the catalytic performance of metallic materials. In recent years, the field of alloy catalysis has made remarkable progress with the emergence of a variety of novel alloy materials and their functions. Therefore, a comprehensive disciplinary framework for catalytic chemistry of alloys that provides a cross-sectional understanding of the broad research field is in high demand. In this review, we provide a comprehensive classification of various alloy materials based on metallurgy, thermodynamics, and inorganic chemistry and summarize the roles of alloying in catalysis and its principles with a brief introduction of the historical background of this research field. Furthermore, we explain how each type of alloy can be used as a catalyst material and how to design a functional catalyst for the target reaction by introducing representative case studies. This review includes two approaches, namely, from materials and reactions, to provide a better understanding of the catalytic chemistry of alloys. Our review offers a perspective on this research field and can be used encyclopedically according to the readers' individual interests.

Recent advances in amorphous electrocatalysts for oxygen evolution reaction

Oxygen evolution reaction (OER) has attracted great attention as an important half-reaction in the electrochemical splitting of water for green hydrogen production. However, the inadequacy of highly efficient and stable electrocatalysts has impeded the development of this technology. Amorphous materials with long-range disordered structures have exhibited superior electrocatalytic performance compared to their crystalline counterparts due to more active sites and higher structural flexibility. This review summarizes the preparation methods of amorphous materials involving oxides, hydroxide, phosphides, sulfides, and their composites, and introduces the recent progress of amorphous OER electrocatalysts in acidic and alkaline media. Finally, the existing challenges and future perspectives for amorphous electrocatalysts for OER are discussed. Therefore, we believe that this review will guide designing amorphous OER electrocatalysts with high performance for future energy applications.

Tailoring Amorphous PdCu Nanostructures for Efficient C-C Cleavage in Ethanol Electrooxidation

The large-scale application of direct ethanol fuel cells has long been obstructed by the sluggish ethanol oxidation reaction at the anode. Current wisdom for designing and fabricating EOR electrocatalysts has been focused on crystalline materials, which result in only limited improvement in catalytic efficiency. Here, we report the amorphous PdCu (a-PdCu) nanomaterials as superior EOR electrocatalysts. The amorphization of PdCu catalysts can significantly facilitate the C-C bond cleavage, which thereby affords a C1 path faradic efficiency as high as 69.6%. Further tailoring the size and shape of a-PdCu nanocatalysts through the delicate kinetic control can result in a maximized mass activity up to 15.25 A/mg_Pd, outperforming most reported catalysts. Notably, accelerated durability tests indicate that both the isotropic structure and one-dimensional shape can dramatically enhance the catalytic durability of the catalysts. This work provides valuable guidance for the rational design and fabrication of amorphous noble metal-based electrocatalysts for fuel cells.

Defect and Interface Engineering of Three-Dimensional Open Nanonetcage Electrocatalysts for Advanced Electrocatalytic Oxygen Evolution Reaction

Defect engineering and interface engineering are two efficient approaches to promote the electrocatalytic performance of transition metal oxides (TMOs) by modulating the local electronic structure and inducing a synergistic effect but usually require costly and complicated processes. Herein, a facile electrochemical etching method is proposed for the controllable tailoring of the defects in a three-dimensional (3D) open nanonetcage CoZnRuO_x heterostructure via the in situ electrochemical etching to remove partial ZnO. The highly open 3D nanostructures, numerous defects, and multicomponent heterointerfaces endow the CoZnRuO_x nanonetcages with more accessible active sites, moderated local electronic structure, and strong synergistic effect, thereby enabling them to not only deliver an ultralow overpotential (244 mV @ 10 mA cm^-2) for oxygen evolution reaction (OER) but also high-performance overall water electrolysis by coupling with commercial Pt/C, with a potential of 1.52 V at 10 mA cm^-2. Moreover, experiments and characterizations also reveal that the remaining Zn²⁺ can facilitate OH^- adsorption and charge transfer, which also further improves the electrocatalytic OER performance. This work proposes a promising strategy for creating surface defects in heterostructured TMOs and provides insights to understand the defect- and interface-induced enhancement of OER electrocatalysis.

Electronegativity Enhanced Strong Metal-Support Interaction in Ru@F-Ni3N for Enhanced Alkaline Hydrogen Evolution

Precious metals (Pt, Ir, Ru, and so on) and related compounds usually demonstrate superb catalytic activity for electrochemical hydrogen production. However, scarcity and stability are still challenges for hydrogen evolution reaction, even for single-atomic-site electrocatalysts. Herein, a fluorine (F) doping strategy is proposed to enhance the strong metal-support interaction between the F-doped Ni₃N support and the loaded ruthenium (Ru) species. Via synergistically modulating both the Ru loading amount and F doping concentration, outstanding HER activity was achieved in Ru@F-Ni₃N with an overpotential (η) of 115 mV at 100 mA cm^-2, superior to the benchmark Pt/C (η = 201 mV). Density functional theory simulation in combination with X-ray photoelectron spectra and X-ray absorption spectroscopy characterizations convincingly demonstrate that, with the strongest electronegativity, F doping could effectively stabilize Ru atoms doped in the F-Ni₃N substrate and simultaneously reduce the H bonding strength, which accelerated the desorption of H₂. These findings provide a facile strategy to modulate both catalytic activities and stabilities of heteroatom-loaded catalytic materials.

Atomically Dispersed CoN3 C1 -TeN1 C3 Diatomic Sites Anchored in N-Doped Carbon as Efficient Bifunctional Catalyst for Synergistic Electrocatalytic Hydrogen Evolution and Oxygen Reduction

A encapsulation-adsorption-pyrolysis strategy for the construction of atomically dispersed Co-Te diatomic sites (DASs) that are anchored in N-doped carbon is reported as an efficient bifunctional catalyst for electrocatalytic hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). The as-constructed catalyst shows the stable CoN₃ C₁ -TeN₁ C₃ coordination structure before and after HER and ORR. The *OOH/*H intermediate species are captured by in situ Raman and in situ attenuated total reflectance-surface enhanced infrared absorption spectroscopy, indicating that the reactant O₂ /H₂ O molecule has a strong interaction with the Co site, revealing that Co^δ+ is an effective active site. Theoretical calculations show that the Co^δ+ has adsorption-activation function and the neighboring Te^δ+ acts as an electron donor adjusting the electronic structure of Co^δ+ , promoting the dissociation of H₂ O molecules and the adsorption of H and oxygen-containing intermediates in HER and ORR. In the meanwhile, the nearest C atom around Co also profoundly affects the adsorption of H atoms. This results in the weakening of the OH adsorption and enhancement of H adsorption, as well as the more stable water molecule dissociation transition state, thus significantly boosting ORR and HER performance.

Nanostructured Metallic Glass in a Highly Upgraded Energy State Contributing to Efficient Catalytic Performance

Metallic glasses (MGs), with high density of low coordination sites and high Gibbs free energy state, are novel promising and competitive candidates in the family of electrochemical catalysts. However, it remains a grand challenge to modify the properties of MGs by control of the disordered atomic structure. Recently, nanostructured metallic glasses (NGs), consisting of amorphous nanometer-sized grains connected by amorphous interfaces, have been reported to exhibit tunable properties compared to the MGs with identical chemical composition. Here, it is demonstrated that electrodeposited Ni-P NG is characterized by an extremely high energy state due to its heterogeneous structure, which significantly promotes the catalytic performance. Moreover, the Ni-P NG with a heterogeneous structure is a perfect precursor for the fabrication of unique honey-like nanoporous structure, which displays superior catalytic performance in the urea oxidation reaction (UOR). Specifically, modified Ni-P NG requires a potential of mere 1.36 V at 10 mA cm^-2 , with a Tafel slope of 13 mV dec^-1 , which is the best UOR performance in Ni-based alloys. The present work demonstrates that the nanostructurization of MGs provides a universal and effective pathway to upgrade the energy state of MGs for the design of high-performance catalysts in energy conversion.

Metal-Organic Framework-Derived Three-Dimensional Macropore Nitrogen-Doped Carbon Frameworks Decorated with Ultrafine Ru-Based Nanoparticles for Overall Water Splitting

Hydrogen energy with the advantages of green, sustainability, and high energy density has been considered as an alternative to fossil fuel energy. Water electrolysis to produce hydrogen is a promising energy conversion technology but limited to the large overpotential; thus, a highly efficient electrocatalyst is urgently needed. Herein, Ru-based electrocatalysts including an ultrathin Ru/three-dimensional (3D) macropore N-doped carbon framework (Ru/3DMNC) and ultrathin RuO₂/3D macropore N-doped carbon framework (RuO₂/3DMNC) are first prepared using a Zn-centered metal-organic framework (MOF, ZIF-8) as the precursor. The ultrathin 3D macropore framework structure together with N doping endows the as-synthesized Ru-based electrocatalysts with abundant exposed catalytic active sites, good electroconductivity, and excellent electron/mass transport, accomplishing improved activities for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting. The Ru/3DMNC and RuO₂/3DMNC present low overpotentials of 50.96 and 216.74 mV to reach a current density of 10 mA cm^-2. Moreover, the overall water splitting device constructed by Ru/3DMNC and RuO₂/3DMNC as the cathode and anode catalysts, respectively, affords a current density of 10 mA cm^-2 only at 1.51 V, which is superior to the Pt/C||RuO₂ cell (1.573 V). This work provides a rational strategy to design and construct the efficient framework structure electrocatalysts for water splitting using MOFs as the precursor.

Identification of Interface Structure for a Topological CoS2 Single Crystal in Oxygen Evolution Reaction with High Intrinsic Reactivity

Transition metal chalcogenides such as CoS₂ have been reported as competitive catalysts for oxygen evolution reaction. It has been well confirmed that surface modification is inevitable in such a process, with the formation of different re-constructed oxide layers. However, which oxide species should be responsible for the optimized catalytic efficiencies and the detailed interface structure between the modified layer and precatalyst remain controversial. Here, a topological CoS₂ single crystal with a well-defined exposed surface is used as a model catalyst, which makes the direct investigation of the interface structure possible. Cross-sectional transmission electron microscopy of the sample reveals the formation of a 2 nm thickness Co₃O₄ layer that grows epitaxially on the CoS₂ surface. Thick CoO pieces are also observed and are loosely attached to the bulk crystal. The compact Co₃O₄ interface structure can result in the fast electron transfer from adsorbed O species to the bulk crystal compared with CoO pieces as evidenced by the electrochemical impedance measurements. This leads to the competitive apparent and intrinsic reactivity of the crystal despite the low surface geometric area. These findings are helpful for the understanding of catalytic origins of transition metal chalcogenides and the designing of high-performance catalysts with interface-phase engineering.

A top-down strategy for amorphization of hydroxyl compounds for electrocatalytic oxygen evolution

Amorphous materials have attracted increasing attention in diverse fields due to their unique properties, yet their controllable fabrications still remain great challenges. Here, we demonstrate a top-down strategy for the fabrications of amorphous oxides through the amorphization of hydroxides. The versatility of this strategy has been validated by the amorphizations of unitary, binary and ternary hydroxides. Detailed characterizations indicate that the amorphization process is realized by the variation of coordination environment during thermal treatment, where the M-OH octahedral structure in hydroxides evolves to M-O tetrahedral structure in amorphous oxides with the disappearance of the M-M coordination. The optimal amorphous oxide (FeCoSn(OH)6-300) exhibits superior oxygen evolution reaction (OER) activity in alkaline media, where the turnover frequency (TOF) value is 39.4 times higher than that of FeCoSn(OH)6. Moreover, the enhanced OER performance and the amorphization process are investigated with density functional theory (DFT) and molecule dynamics (MD) simulations. The reported top-down fabrication strategy for fabricating amorphous oxides, may further promote fundamental research into and practical applications of amorphous materials for catalysis.

Single-site Pt-doped RuO2 hollow nanospheres with interstitial C for high-performance acidic overall water splitting

Realizing stable and efficient overall water splitting is highly desirable for sustainable and efficient hydrogen production yet challenging because of the rapid deactivation of electrocatalysts during the acidic oxygen evolution process. Here, we report that the single-site Pt-doped RuO₂ hollow nanospheres (SS Pt-RuO₂ HNSs) with interstitial C can serve as highly active and stable electrocatalysts for overall water splitting in 0.5 M H₂SO₄. The performance toward overall water splitting have surpassed most of the reported catalysts. Impressively, the SS Pt-RuO₂ HNSs exhibit promising stability in polymer electrolyte membrane electrolyzer at 100 mA cm^-2 during continuous operation for 100 hours. Detailed experiments reveal that the interstitial C can elongate Ru-O and Pt-O bonds, and the presence of SS Pt can readily vary the electronic properties of RuO₂ and improve the OER activity by reducing the energy barriers and enhancing the dissociation energy of ^*O species.

Engineering Heterostructured Pd-Bi2Te3 Doughnut/Pd Hollow Nanospheres for Ethylene Glycol Electrooxidation

The electrooxidation of ethylene glycol (EG) is of vital significance for the conversion from biomass energy into electrical energy via direct fuel cells. However, the EG oxidation reaction (EGOR) suffers from poor efficiency due to the limitation of high-performance electrocatalysts for cleaving the C-C bonds. Herein, this limitation is successfully addressed by fabricating the doughnut-shaped Pd-Bi₂Te₃ heterostructured catalyst. Notably, the heterojunction Pd-Bi₂Te₃ nanocatalyst has been demonstrated to be highly active toward the EGOR with superb activity and durability, in which a mass activity as high as 2420.8 mA mg^-1 is achieved in alkaline media, being 1.7 times higher than that of the commercial Pd/C catalyst. Upon combination of experimental results with mechanism studies, it is indicated that the remarkable EGOR performance is attributed to the enlarged active areas that stemmed from the doughnut-like structure, as well as the strong synergistic effect from Pd-Bi₂Te₃ and Pd. More importantly, the highly electroactive Pd-Bi₂Te₃ can accelerate charge transfer and boost the oxidation of CO-like intermediates, which are conducive to the enhancement in electrochemical stability.

Engineering transition metal catalysts for large-current-density water splitting

Electrochemical water splitting plays a crucial role in transferring electricity to hydrogen fuel and appropriate electrocatalysts are crucial to satisfy the strict industrial demand. However, the successfully developed non-noble metal catalysts have a small tested range and the current density is usually less than 100 mA cm^-2, which is still far away from the practical application standards. Aiming to provide guidance for the fabrication of more advanced electrocatalysts with a large current density, we herein systematically summarize the recent progress achieved in the field of cost-efficient and large-current-density electrocatalyst design. Beginning by illustrating the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) mechanisms, we elaborate on the concurrent issues of non-noble metal catalysts that are required to be addressed. In view of large-current-density operating conditions, some distinctive features with regard to good electrical conductivity, high intrinsic activity, rich active sites, and porous architecture are also summarized. Next, some representative large-current-density electrocatalysts are classified. Finally, we discuss the challenges associated with large-current-density water electrolysis and future pathways in the hope of guiding the future development of more efficient non-noble-metal catalysts to boost large-scale hydrogen production with less electricity consumption.

Strategies for Electrochemically Sustainable H2 Production in Acid

Acidified water electrolysis with fast kinetics is widely regarded as a promising option for producing H2 . The main challenge of this technique is the difficulty in realizing sustainable H2 production (SHP) because of the poor stability of most electrode catalysts, especially on the anode side, under strongly acidic and highly polarized electrochemical environments, which leads to surface corrosion and performance degradation. Research efforts focused on tuning the atomic/nano structures of catalysts have been made to address this stability issue, with only limited effectiveness because of inevitable catalyst degradation. A systems approach considering reaction types and system configurations/operations may provide innovative viewpoints and strategies for SHP, although these aspects have been overlooked thus far. This review provides an overview of acidified water electrolysis for systematic investigations of these aspects to achieve SHP. First, the fundamental principles of SHP are discussed. Then, recent advances on design of stable electrode materials are examined, and several new strategies for SHP are proposed, including fabrication of symmetrical heterogeneous electrolysis system and fluid homogeneous electrolysis system, as well as decoupling/hybrid-governed sustainability. Finally, remaining challenges and corresponding opportunities are outlined to stimulate endeavors toward the development of advanced acidified water electrolysis techniques for SHP.

Crystal Structure Control of Binary and Ternary Solid-Solution Alloy Nanoparticles with a Face-Centered Cubic or Hexagonal Close-Packed Phase

The crystal structure significantly affects the physical and chemical properties of solids. However, the crystal structure-dependent properties of alloys are rarely studied because controlling the crystal structure of an alloy at the same composition is extremely difficult. Here, for the first time, we successfully demonstrate the synthesis of binary Ru-Pt (Ru/Pt = 7:3) and Ru-Ir (Ru/Ir = 7:3) and ternary Ru-Ir-Pt (Ru/Ir/Pt = 7:1.5:1.5) solid-solution alloy nanoparticles (NPs) with well-controlled hexagonal close-packed (hcp) and face-centered cubic (fcc) phases, through the chemical reduction method. The crystal structure control is realized by precisely tunning the reduction speeds of the metal precursors. The effect of the crystal structure on the catalytic performance of solid-solution alloy NPs is systematically investigated. Impressively, all the hcp alloy NPs show superior electrocatalytic activities for the hydrogen evolution reaction in alkaline solution compared with the fcc alloy NPs. In particular, hcp-RuIrPt exhibits extremely high intrinsic (mass) activity, which is 3.1 (3.2) and 6.7 (6.9) times enhanced compared to that of fcc-RuIrPt and commercial Pt/C.

Surprisingly Low Reactivity of Layered Manganese Oxide toward Water Oxidation in Fe/Ni-Free Electrolyte under Alkaline Conditions

So far, many studies on the oxygen-evolution reaction (OER) by Mn oxides have been focused on activity; however, the identification of the best performing active site and corresponding catalytic cycles is also of critical importance. Herein, the real intrinsic activity of layered Mn oxide toward OER in Fe/Ni-free KOH is studied for the first time. At pH ≈ 14, the onset of OER for layered Mn oxide in the presence of Fe/Ni-free KOH happens at 1.72 V (vs reversible hydrogen electrode (RHE)). In the presence of Fe ions, a 190 mV decrease in the overpotential of OER was recorded for layered Mn oxide as well as a significant decrease (from 172.8 to 49 mV/decade) in the Tafel slope. Furthermore, we find that both Ni and Fe ions increase OER remarkably in the presence of layered Mn oxide, but that pure layered Mn oxide is not an efficient catalyst for OER without Ni and Fe under alkaline conditions. Thus, pure layered Mn oxide and electrolytes are critical factors in finding the real intrinsic activity of layered Mn oxide for OER. Our results call into question the high efficiency of layered Mn oxides toward OER under alkaline conditions and also elucidate the significant role of Ni and Fe impurities in the electrolyte in the presence of layered Mn oxide toward OER under alkaline conditions. Overall, a computational model supports the conclusions from the experimental structural and electrochemical characterizations. In particular, substitutional doping with Fe decreases the thermodynamic OER overpotential up to 310 mV. Besides, the thermodynamic OER onset potential calculated for the Fe-free structures is higher than 1.7 V (vs RHE) and, thus, not in the stability range of Mn oxides.

CO2-assisted synthesis of crystalline/amorphous NiFe-MOF heterostructure for high-efficiency electrocatalytic water oxidation

Modulating the crystalline phase and structure of metal organic frameworks (MOFs) for superior electrocatalytic oxygen evolution reaction (OER) performance is a significant but challenging topic. Herein, a facile CO2-assisted strategy...

Synergistic phase and crystallinity engineering in cubic RuSe2 catalysts towards efficient hydrogen evolution reaction

Herein, cubic RuSe2 electrocatalysts with different 1T phase ratios (ranging from 20.53% to 64.97%) and crystallinities (ranging from 1.72% to 89.10%) were developed by a fast and efficient microwave-assisted synthesis method.

Unraveling the Function of Metal-Amorphous Support Interactions in Single-Atom Electrocatalytic Hydrogen Evolution

Amorphization of support in single-atoms catalysts is a less researched concept for promoting catalytic kinetics through modulating the metal-support interaction (MSI). We modeled single-atom ruthenium (Ru SAs ) supported on amorphous cobalt/nickel (oxy)hydroxide (Ru-a-CoNi) to explore the favorable MSI between Ru SAs and amorphous skeleton for alkaline hydrogen evolution reaction (HER). Differing from the usual crystal counterpart (Ru-c-CoNi), the electrons on Ru SAs are facilitated to exchange among local configurations (Ru-O-Co/Ni) of Ru-a-CoNi since flexibly amorphous configuration induces the possible d-d electrons transfer and medium-to-long range p-π orbitals coupling, further intensifying the MSI. It enables Ru-a-CoNi with enhanced water dissociation, alleviated oxophilicity, and rapid hydrogen migration, which results in superior durability and HER activity of Ru-a-CoNi, wherein only 15 mV can deliver 10 mA cm - 2 , significantly lower than 58 mV of Ru-c-CoNi.

Metal and metal oxide amorphous nanomaterials towards electrochemical applications

Amorphous nanomaterials have aroused extensive interest due to their unique properties. Their performance is highly related with their distinct atomic arrangements, which have no long-range order but possess short- to medium-range order. Herein, an overview of state-of-the-art synthesis methods of amorphous nanomaterials, structural characteristics and their electrochemical properties is presented. Advanced characterization methods for analyzing and proving the local order of amorphous structures, such as X-ray absorption fine structure spectroscopy, atomic electron tomography and nanobeam electron diffraction, are introduced. Various synthesis strategies for amorphous nanomaterials are covered, especially the salt-assisted metal organic decomposition method to prepare ultrathin amorphous nanosheets. Furthermore, the design and structure-activity relationship of amorphous nanomaterials towards electrochemical applications, including electrocatalysts and battery anode/cathode materials, is discussed.

Amorphous materials for elementary-gas-involved electrocatalysis: an overview

Given the critical demands on energy conversion, storage, and transportation, tremendous interest has been devoted to the field of material development related to energy harvesting, recently. As the only route towards energy utilization, the carriers with the characteristics of low carbon are regarded as the future choice, e.g., hydrogen and ammonia. To this end, electrocatalysis provides a green way to access these substances. However, the unfulfilled conversion efficiency is the bottleneck for practical application. In this review, the promising characteristics of amorphous materials and the amorphous-induced electrocatalytic enhancement (AIEE) were emphasized. In the beginning, the characteristics of amorphous materials are briefly summarized. The basic mechanism of heterogeneous electrocatalytic reactions is illustrated, including the hydrogen/oxygen evolution and oxygen/nitrogen reduction. In the third part, the electrocatalytic performance of amorphous materials is discussed in detail, and the mechanism of AIEE is highlighted. In the last section of this review, the challenges and outlook for the development of amorphous enhanced electrocatalysis are presented.

Recent Progress in Advanced Electrocatalyst Design for Acidic Oxygen Evolution Reaction

Proton exchange membrane (PEM) water electrolyzers hold great significance for renewable energy storage and conversion. The acidic oxygen evolution reaction (OER) is one of the main roadblocks that hinder the practical application of PEM water electrolyzers. Highly active, cost-effective, and durable electrocatalysts are indispensable for lowering the high kinetic barrier of OER to achieve boosted reaction kinetics. To date, a wide spectrum of advanced electrocatalysts has been designed and synthesized for enhanced acidic OER performance, though Ir and Ru based nanostructures still represent the state-of-the-art catalysts. In this Progress Report, recent research progress in advanced electrocatalysts for improved acidic OER performance is summarized. First, fundamental understanding about acidic OER including reaction mechanisms and atomic understanding to acidic OER for rational design of efficient electrocatalysts are discussed. Thereafter, an overview of the progress in the design and synthesis of advanced acidic OER electrocatalysts is provided in terms of catalyst category, i.e., metallic nanostructures (Ir and Ru based), precious metal oxides, nonprecious metal oxides, and carbon based nanomaterials. Finally, perspectives to the future development of acidic OER are provided from the aspects of reaction mechanism investigation and more efficient electrocatalyst design.

Electrocatalytic Oxygen Evolution Reaction in Acidic Conditions: Recent Progress and Perspectives

The electrochemical oxygen evolution reaction (OER) is an important half-cell reaction in many renewable energy conversion and storage technologies, including electrolyzers, nitrogen fixation, CO₂ reduction, metal-air batteries, and regenerative fuel cells. Among them, proton exchange membrane (PEM)-based devices exhibit a series of advantages, such as excellent proton conductivity, high durability, and good mechanical strength, and have attracted global interest as a green energy device for transport and stationary sectors. Nevertheless, with a view to rapid commercialization, it is urgent to develop highly active and acid-stable OER catalysts for PEM-based devices. In this Review, based on the recent advances in theoretical calculation and in situ/operando characterization, the OER mechanism in acidic conditions is first discussed in detail. Subsequently, recent advances in the development of several types of acid-stable OER catalysts, including noble metals, non-noble metals, and even metal-free OER materials, are systematically summarized. Finally, the current key issues and future challenges for materials used as acidic OER catalysis are identified and potential future directions are proposed.

Single Iridium Atom Doped Ni2P Catalyst for Optimal Oxygen Evolution

Single-atom catalysts (SACs) with 100% active sites have excellent prospects for application in the oxygen evolution reaction (OER). However, further enhancement of the catalytic activity for OER is quite challenging, particularly for the development of stable SACs with overpotentials <180 mV. Here, we report an iridium single atom on Ni₂P catalyst (Ir_SA-Ni₂P) with a record low overpotential of 149 mV at a current density of 10 mA·cm^-2 in 1.0 M KOH. The Ir_SA-Ni₂P catalyst delivers a current density up to ∼28-fold higher than that of the widely used IrO₂ at 1.53 V vs RHE. Both the experimental results and computational simulations indicate that Ir single atoms preferentially occupy Ni sites on the top surface. The reconstructed Ir-O-P/Ni-O-P bonding environment plays a vital role for optimal adsorption and desorption of the OER intermediate species, which leads to marked enhancement of the OER activity. Additionally, the dynamic "top-down" evolution of the specific structure of the Ni@Ir particles is responsible for the robust single-atom structure and, thus, the stability property. This Ir_SA-Ni₂P catalyst offers novel prospects for simplifying decoration strategies and further enhancing OER performance.

Advanced Transition Metal-Based OER Electrocatalysts: Current Status, Opportunities, and Challenges

Oxygen evolution reaction (OER) is an important half-reaction involved in many electrochemical applications, such as water splitting and rechargeable metal-air batteries. However, the sluggish kinetics of its four-electron transfer process becomes a bottleneck to the performance enhancement. Thus, rational design of electrocatalysts for OER based on thorough understanding of mechanisms and structure-activity relationship is of vital significance. This review begins with the introduction of OER mechanisms which include conventional adsorbate evolution mechanism and lattice-oxygen-mediated mechanism. The reaction pathways and related intermediates are discussed in detail, and several descriptors which greatly assist in catalyst screen and optimization are summarized. Some important parameters suggested as measurement criteria for OER are also mentioned and discussed. Then, recent developments and breakthroughs in experimental achievements on transition metal-based OER electrocatalysts are reviewed to reveal the novel design principles. Finally, some perspectives and future directions are proposed for further catalytic performance enhancement and deeper understanding of catalyst design. It is believed that iterative improvements based on the understanding of mechanisms and fundamental design principles are essential to realize the applications of efficient transition metal-based OER electrocatalysts for electrochemical energy storage and conversion technologies.

Anion Modulation of Pt-Group Metals and Electrocatalysis Applications

Pt-group metal (PGM) electrocatalysts with unique electronic structures and irreplaceable comprehensive properties play crucial roles in electrocatalysis. Anion engineering can create a series of PGM compounds (such as RuP₂ , IrP₂ , PtP₂ , RuB₂ , Ru₂ B₃ , RuS₂ , etc.) that provide a promising prospect for improving the electrocatalytic performance and use of Pt-group noble metals. This review seeks the electrochemical activity origin of anion-modulated PGM compounds, and systematically analyzes and summarizes their synthetic strategies and energy-relevant applications in electrocatalysis. Orientation towards the sustainable development of nonfossil resources has stimulated a blossoming interest in the design of advanced electrocatalysts for clean energy conversion. The anion-modulated strategy for Pt-group metals (PGMs) by means of anion engineering possesses high flexibility to regulate the electronic structure, providing a promising prospect for constructing electrocatalysts with superior activity and stability to satisfy a future green electrochemical energy conversion system. Based on the previous work of our group and others, this review summarizes the up-to-date progress on anion-modulated PGM compounds (such as RuP₂ , IrP₂ , PtP₂ , RuB₂ , Ru₂ B₃ , RuS₂ , etc.) in energy-related electrocatalysis from the origin of their activity and synthetic strategies to electrochemical applications including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), N₂ reduction reaction (NRR), and CO₂ reduction reaction (CO₂ RR). At the end, the key problems, countermeasures and future development orientations of anion-modulated PGM compounds toward electrocatalytic applications are proposed.

Sodium-Decorated Amorphous/Crystalline RuO2 with Rich Oxygen Vacancies: A Robust pH-Universal Oxygen Evolution Electrocatalyst

The oxygen evolution reaction (OER) is a key reaction for many electrochemical devices. To date, many OER electrocatalysts function well in alkaline media, but exhibit poor performances in neutral and acidic media, especially the acidic stability. Herein, sodium-decorated amorphous/crystalline RuO₂ with rich oxygen vacancies (a/c-RuO₂ ) was developed as a pH-universal OER electrocatalyst. The a/c-RuO₂ shows remarkable resistance to acid corrosion and oxidation during OER, which leads to an extremely high catalytic stability, as confirmed by a negligible overpotential increase after continuously catalyzing OER for 60 h at pH=1. Besides, a/c-RuO₂ also exhibits superior OER activities to commercial RuO₂ and most reported OER catalysts under all pH conditions. Theoretical calculations indicated that the introduction of Na dopant and oxygen vacancy in RuO₂ weakens the adsorption strength of the OER intermediates by engineering the d-band center, thereby lowering the energy barrier for OER.