Facilitating alkaline hydrogen evolution reaction on the hetero-interfaced Ru/RuO2 through Pt single atoms doping.

Exploring an active and cost-effective electrocatalyst alternative to carbon-supported platinum nanoparticles for alkaline hydrogen evolution reaction (HER) have remained elusive to date. Here, we report a catalyst based on platinum single atoms (SAs) doped into the hetero-interfaced Ru/RuO2 support (referred to as Pt-Ru/RuO2), which features a low HER overpotential, an excellent stability and a distinctly enhanced cost-based activity compared to commercial Pt/C and Ru/C in 1 M KOH. Advanced physico-chemical characterizations disclose that the sluggish water dissociation is accelerated by RuO2 while Pt SAs and the metallic Ru facilitate the subsequent H* combination. Theoretical calculations correlate with the experimental findings. Furthermore, Pt-Ru/RuO2 only requires 1.90 V to reach 1 A cm-2 and delivers a high price activity in the anion exchange membrane water electrolyzer, outperforming the benchmark Pt/C. This research offers a feasible guidance for developing the noble metal-based catalysts with high performance and low cost toward practical H2 production.

Recent Progress in 2D Metal-Organic Framework-Related Materials.

2D metal-organic frameworks-based (2D MOF-related) materials benefit from variable topological structures, plentiful open active sites, and high specific surface areas, demonstrating promising applications in gas storage, adsorption and separation, energy conversion, and other domains. In recent years, researchers have innovatively designed multiple strategies to avoid the adverse effects of conventional methods on the synthesis of high-quality 2D MOFs. This review focuses on the latest advances in creative synthesis techniques for 2D MOF-related materials from both the top-down and bottom-up perspectives. Subsequently, the strategies are categorized and summarized for synthesizing 2D MOF-related composites and their derivatives. Finally, the current challenges are highlighted faced by 2D MOF-related materials and some targeted recommendations are put forward to inspire researchers to investigate more effective synthesis methods.

2D MOF-assisted Pyrolysis-displacement-alloying Synthesis of High-entropy Alloy Nanoparticles Library for Efficient Electrocatalytic Hydrogen Oxidation.

Multimetallic alloy nanoparticles (NPs) have received considerable attention in various applications due to their compositional variability and exceptional properties. However, the complexity of both the general synthesis and structure-activity relationships remain the long-standing challenges in this field. Herein, we report a versatile 2D MOF-assisted pyrolysis-displacement-alloying route to successfully synthesize a series of binary, ternary and even high-entropy NPs that are uniformly dispersed on porous nitrogen-doped carbon nanosheets (PNC NSs). As a proof of utility, the obtained Co0.2 Ru0.7 Pt0.1 /PNC NSs exhibits apparent hydrogen oxidation activity and durability with a record-high mass specific kinetic current of 1.84 A mg-1 at the overpotential of 50 mV, which is approximately 11.5 times higher than that of the Pt benchmark. Both experimental and theoretical studies reveal that the addition of Pt engenders a phase transition in CoRu alloys from hexagonal close-packed (hcp) to face-centered cubic (fcc) structure. The elevated reactivity of the resulted ternary alloy can be attributed to the optimized adsorption of hydrogen intermediate and the decreased reaction barrier for water formation. This study opens a new avenue for the development of highly efficient alloy NPs with various compositions and functions.

Synergistic Mechanism of Sub-Nanometric Ru Clusters Anchored on Tungsten Oxide Nanowires for High-Efficient Bifunctional Hydrogen Electrocatalysis.

The construction of strong interactions and synergistic effects between small metal clusters and supports offers a great opportunity to achieve high-performance and cost-effective heterogeneous catalysis, however, studies on its applications in electrocatalysis are still insufficient. Herein, it is reported that W18 O49 nanowires supported sub-nanometric Ru clusters (denoted as Ru SNC/W18 O49 NWs) constitute an efficient bifunctional electrocatalyst for hydrogen evolution/oxidation reactions (HER and HOR) under acidic condition. Microstructural analyses, X-ray absorption spectroscopy, and density functional theory (DFT) calculations reveal that the Ru SNCs with an average RuRu coordination number of 4.9 are anchored to the W18 O49 NWs via RuOW bonds at the interface. The strong metal-support interaction leads to the electron-deficient state of Ru SNCs, which enables a modulated RuH strength. Furthermore, the unique proton transport capability of the W18 O49 also provides a potential migration channel for the reaction intermediates. These components collectively enable the remarkable performance of Ru SNC/W18 O49 NWs for hydrogen electrocatalysis with 2.5 times of exchange current density than that of carbon-supported Ru nanoparticles, and even rival the state-of-the-art Pt catalyst. This work provides a new prospect for the development of supported sub-nanometric metal clusters for efficient electrocatalysis.

Stable and Ordered Body-Centered Cubic PdCu Phase for Highly Selective Hydrogenation.

Phase engineering of nanomaterials plays a crucial role for regulating the catalytic performance. Nevertheless, great challenges still remain for elucidating the structure-selectivity correlation. Herein, this study demonstrates that the body-centered cubic phase of PdCu (bcc-PdCu) can serve as a highly active and selective catalyst for 3-nitrostyrene (NS) hydrogenation under mild conditions. In particular, bcc-PdCu displays a 3-nitro-ethylbenzene (NE) selectivity of 93.8% with a turnover frequency (TOF) value of 4573 h-1 at 30 °C in the presence of H2 . With the assistance of NH3 ∙BH3 , the selectivity of 3-amino-styrene (AS) reaches 94.5% with a TOF value of 13 719 h-1 . Detailed experimental and theoretical calculations reveal that improved NE selectivity is ascribed to the selective adsorption of the CC bond and desorption of NE on bcc-PdCu. Moreover, the presence of NH3 ∙BH3 facilitates the selective hydrogenation of NO2 due to their strong interaction and thus leads to the formation of AS. This work provides an efficient selective catalyst for NS hydrogenation under mild conditions, which may attract immediate interests in the fields of materials, chemistry, and catalysis.

MXene-Copper/Cobalt Hybrids via Lewis Acidic Molten Salts Etching for High Performance Symmetric Supercapacitors.

MXenes have attracted great interests as supercapacitors due to their metallic conductivity, high density, and hydrophilic nature. Herein we report Ti3 C2 -Cu/Co hybrids via molten salt etching in which the existence of metal atoms and their interactions with MXene via surficial O atoms were elucidated by XAFS for the first time. The electrochemical investigation of Ti3 C2 -Cu electrode demonstrated the pseudocapacitive contribution of Cu and a splendid specific capacitance of 885.0 F g-1 at 0.5 A g-1 in 1.0 M H2 SO4 . Symmetric supercapacitor Ti3 C2 -Cu//Ti3 C2 -Cu was demonstrated with operating voltage of 1.6 V, areal capacitance of 290.5 mF cm-2 at 1 mA cm-2 , and stability over 10 000 cycles. It delivered an areal energy density of 103.3 µWh cm-2 at power density of 0.8 mW cm-2 , based on which a supercapacitor pouch was fabricated. It provides deeper insights into the molten salt mechanism and strategies for designing MXene-based materials for electrochemical energy storage.

Compressive Strain in N-Doped Palladium/Amorphous-Cobalt (II) Interface Facilitates Alkaline Hydrogen Evolution.

The development of palladium-based catalysts for alkaline hydrogen evolution reaction (HER) is highly desired for renewable hydrogen energy systems, yet still challenging due to the strong palladium-hydrogen bond. Herein, the bottleneck is largely overcome by constructing a nitridation-induced compressively strained-interface N-doped palladium/amorphous cobalt (II) interface (N-Pd/A-Co(II)), which dramatically boosts HER performance in alkaline condition. The optimized catalyst with the compressive strain of 2.7% exhibits the higher activity with an overpotential of only 58 mV to achieve the current density of 10 mA cm-2 , much better than those of pure Pd (327 mV), and the state-of-art Pt/C (78 mV). Notably, it also shows excellent stability with negligible decline during a 30 h stability test. Detailed analyses reveal that the strong absorption of Hads on Pd can be efficiently reduced via the compressively strained N-doped Pd. And the amorphous Co(II) component accelerates the water dissociation. Consequently, the cooperative effect between the compressed N-doped Pd and amorphous Co(II) creates the impressive HER performance in alkaline condition, highlighting the importance of the functional interface to develop efficient electrocatalysts for HER and beyond.

Spin Regulation on 2D Pd-Fe-Pt Nanomeshes Promotes Fuel Electrooxidations.

Spin engineering provides a powerful strategy for manipulating the interaction between electrons in the d orbital and oxygen-containing adsorbates, while a little endeavor was performed to understand whether such a strategy can make a prosperous enhancement for fuel electrooxidations. Herein, we demonstrate that spin engineering of trimetallic Pd-Fe-Pt nanomeshes (NMs) can achieve superior enhancement for fuel electrooxidations. Magnetization characterizations reveal that Pd59Fe27Pt14 NMs own the highest number of polarized spins (µb = 0.85 µB/f.u.), playing an important role on facilitating the adsorption of OHads to promote the oxidation of COads, as confirmed by theoretical results. Consequently, the optimized Pd59Fe27Pt14 NMs exhibit excellent methanol oxidation reaction activity and stability with a mass activity of 1.61 A mgPt-1, 2.6-fold and 7.3-fold larger than those of PtRu/C and Pt/C. Such catalysts also present exceptional performances in ethanol oxidation and formic acid oxidation reactions. Our work highlights a new strategy for designing efficient electrocatalysts for fuel electrooxidations and beyond.

Partially hydroxylated ultrathin iridium nanosheets as efficient electrocatalysts for water splitting.

Ultrathin two-dimensional (2D) materials have attracted considerable attention for their unique physicochemical properties and promising applications; however, preparation of freestanding ultrathin 2D noble metal remains a significant challenge. Here, for the first time, we report use of a wet-chemical method to synthesize partially hydroxylated ultrathin Ir nanosheets (Ir-NSs) of only five to six atomic layers' thickness. Detailed analysis indicates that the growth confinement effect of carbon monoxide and the partially hydroxylated surface play a critical role in formation of the ultrathin structure. The ultrathin Ir-NSs exhibit excellent performance for both the hydrogen evolution reaction and oxygen evolution reaction in a wide pH range, outperforming the state-of-the-art Pt/C and IrO2, respectively. Density-functional theory calculations reveal that the partial hydroxylation not only enhances the surface electron transfer between Ir-sites and intermediate O-species, but also guarantees efficient initial activation of bond cleavage of H-O-H for first-step H2O splitting. This, ultimately, breaks through barriers to full water splitting, with efficient electron transfer essentially maintained.

Double Perovskite LaFex Ni1-x O3 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 LaFex Ni1-x O3 (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.

Phase and structure engineering of copper tin heterostructures for efficient electrochemical carbon dioxide reduction.

While engineering the phase and structure of electrocatalysts could regulate the performance of many typical electrochemical processes, its importance to the carbon dioxide electroreduction has been largely unexplored. Herein, a series of phase and structure engineered copper-tin dioxide catalysts have been created and thoroughly exploited for the carbon dioxide electroreduction to correlate performance with their unique structures and phases. The copper oxide/hollow tin dioxide heterostructure catalyst exhibits promising performance, which can tune the products from carbon monoxide to formic acid at high faradaic efficiency by simply changing the electrolysis potentials from -0.7 VRHE to -1.0 VRHE. The excellent performance is attributed to the abundant copper/tin dioxide interfaces involved in the copper oxide/hollow tin dioxide heterostructure during the electrochemical process, decreasing the reaction free-energies for the formation of COOH* species. Our work reported herein emphasizes the importance of phase and structure modulating of catalysts for enhancing electrochemical CO2 reduction and beyond.

Dynamic Structure Evolution of Composition Segregated Iridium-Nickel Rhombic Dodecahedra toward Efficient Oxygen Evolution Electrocatalysis.

The anodic oxygen evolution reaction (OER) is central to various energy conversion devices, but the investigation of the dynamic evolution of catalysts in different OER conditions remains quite limited, which is unfavorable for the understanding of the actual structure-activity relationship and catalyst optimization. Herein, we constructed monodispersed IrNi x nanoparticles (NPs) with distinct composition-segregated features and captured their structural evolution in various OER environments. We decoded the interesting self-reconstruction of IrNi x NPs during the OER, in which an Ir-skin framework is generated in an acidic electrolyte, while a Ni-rich surface layer is observed in an alkaline electrolyte owing to Ni migration. Benefiting from such self-reconstruction, considerable OER enhancements are achieved under both acidic and alkaline conditions. For comparison, IrNi x nanoframes with Ir skins prepared by chemical etching show a similar structural evolution result in the acidic electrolyte, but a total different phenomenon in the alkaline electrolyte. By tracking the structural evolution of IrNi x catalysts and correlating them with OER activity trajectories, the present work provides a significant understanding for designing efficient OER catalysts with controlled compositional distributions.

Enhancing Oxygen Evolution Electrocatalysis via the Intimate Hydroxide-Oxide Interface.

The development of electrocatalysts with high activity and stability for oxygen evolution reaction (OER) is critically important, the one being regarded as the bottleneck process of overall water splitting. Herein, we fulfill significant OER improvement in both activity and stability by constructing a class of Ni(OH)2-CeO2 supported on carbon paper (Ni xCe y@CP) with an intimate hydroxide (Ni(OH)2)-oxide (CeO2) interface. Such interface largely promotes the OER activity with a low overpotential of 220 mV at 10 mA cm-2 and a small Tafel slope of 81.9 mV dec-1 in 1 M KOH. X-ray photoelectron spectroscopy analysis shows that the intimate interface induced by the strong electronic interactions between Ni(OH)2 and CeO2 involves the modulation of binding strength between intermediates and catalysts, making a great contribution to the OER enhancement. Importantly, such intimate interface structures can be largely maintained even after a long-time stability test. We have further demonstrated that, when pairing the Ni4Ce1@CP after phosphorization (P-Ni4Ce1@CP), the Ni4Ce1@CP and P-Ni4Ce1@CP assembly is highly active and stable for overall water splitting with a low voltage of 1.68 V at 25 mA cm-2 and negligible stability delay over 30 h of continuous operation, which are much better than the commercial Ir/C and Pt/C.

Ultrathin Vein-Like Iridium-Tin Nanowires with Abundant Oxidized Tin as High-Performance Ethanol Oxidation Electrocatalysts.

Iridium (Ir) holds great promise for ethanol oxidation reaction (EOR), while its practical applications suffer from the limited shape-controlled synthesis due to its low-energy barrier for nucleation. To overcome this limitation, the preparation of a new class of ultrathin vein-like Ir-tin nanowires (IrSn NWs) with abundant oxidized Sn is reported. By tuning the ratio of Ir to Sn, the optimized Ir67 Sn33 /C exhibits the highest mass density of 95.6 mA mg-1 Ir for EOR at low potential (0.04 V), which is 4.1-fold and 20-fold higher than that of Ir/C and the commercial Pt/C, respectively. It also exhibits the smallest Tafel slope of 153 mV dec-1 and superior stability after 2 h chronoamperometric measurement. Electrochemical measurements and X-ray photoelectron spectra results confirm that the abundant oxidized Sn promotes a complete oxidization of ethanol into CO2 at low potential. This work highlights the importance of non-noble metal on enhancing the EOR performance.

A Cost-Efficient Bifunctional Ultrathin Nanosheets Array for Electrochemical Overall Water Splitting.

The design of cost-efficient earth-abundant catalysts with superior performance for the electrochemical water splitting is highly desirable. Herein, a general strategy for fabricating superior bifunctional water splitting electrodes is reported, where cost-efficient earth-abundant ultrathin Ni-based nanosheets arrays are directly grown on nickel foam (NF). The newly created Ni-based nanosheets@NF exhibit unique features of ultrathin building block, 3D hierarchical structure, and alloy effect with the optimized Ni5 Fe layered double hydroxide@NF (Ni5 Fe LDH@NF) exhibiting low overpotentials of 210 and 133 mV toward both oxygen evolution reaction and hydrogen evolution reaction at 10 mA cm-2 in alkaline condition, respectively. More significantly, when applying as the bifunctional overall water splitting electrocatalyst, the Ni5 Fe LDH@NF shows an appealing potential of 1.59 V at 10 mA cm-2 and also superior durability at the very high current density of 50 mA cm-2 .

Trimetallic Oxyhydroxide Coralloids for Efficient Oxygen Evolution Electrocatalysis.

Trimetallic oxyhydroxides are one of the most effective materials for oxygen evolution reaction (OER) catalysis, a key process for water splitting. Herein, we describe a facile wet-chemical method to directly grow a series of coralloid trimetallic oxyhydroxides on arbitrary substrates such as nickel foam (NF) and carbon nanotubes (CNTs). The amount of iron in these oxyhydroxide sponges on NF and CNTs was precisely controlled, revealing that the electrocatalytic activity of the WCoFe trimetallic oxyhydroxides depends on the Fe amount in a volcano-like fashion. The optimized W0.5 Co0.4 Fe0.1 /NF catalyst exhibited an overpotential of only 310 mV to deliver a large current density of 100 mA cm-2 and a very low Tafel slope of 32 mV dec-1 . It also showed superior stability with negligible activity decay after use in the OER for 21 days (>500 h). X-ray photoelectron spectroscopy revealed that the addition of Fe leads to an on average lower Co oxidation state, which contributes to the enhanced OER performance.

Ultrathin Laminar Ir Superstructure as Highly Efficient Oxygen Evolution Electrocatalyst in Broad pH Range.

Shape-controlled noble metal nanocrystals (NCs), such as Au, Ag, Pt, Pd, Ru, and Rh are of great success due to their new and enhanced properties and applications in chemical conversion, fuel cells, and sensors, but the realization of shape control of Ir NCs for achieving enhanced electrocatalysis remains a significant challenge. Herein, we report an efficient solution method for a new class of three-dimensional (3D) Ir superstructure that consists of ultrathin Ir nanosheets as subunits. Electrochemical studies show that it delivers the excellent electrocatalytic activity toward oxygen evolution reaction (OER) in alkaline condition with an onset potential at 1.43 V versus reversible hydrogen electrode (RHE) and a very low Tafel slope of 32.7 mV decade(-1). In particular, it even shows superior performance for OER in acidic solutions with the low onset overpotential of 1.45 V versus RHE and small Tafel slope of 40.8 mV decade(-1), which are much better than those of small Ir nanoparticles (NPs). The 3D Ir superstructures also exhibit good stability under acidic condition with the potential shift of less than 20 mV after 8 h i-t test. The present work highlights the importance of tuning 3D structures of Ir NCs for enhancing OER performance.