Developing robust non-platinum electrocatalysts with multifunctional active sites for pH-universal hydrogen evolution reaction (HER) is crucial for scalable hydrogen production through electrochemical water splitting. Here ultra-small ruthenium-nickel alloy nanoparticles steadily anchored on reduced graphene oxide papers (Ru-Ni/rGOPs) as versatile electrocatalytic materials for acidic and alkaline HER are reported. These Ru-Ni alloy nanoparticles serve as pH self-adaptive electroactive species by making use of in situ surface reconstruction, where surface Ni atoms are hydroxylated to produce bifunctional active sites of Ru-Ni(OH)2 for alkaline HER, and selectively etched to form monometallic Ru active sites for acidic HER, respectively. Owing to the presence of Ru-Ni(OH)2 multi-site surface, which not only accelerates water dissociation to generate reactive hydrogen intermediates but also facilitates their recombination into hydrogen molecules, the self-supported Ru90Ni10/rGOP hybrid electrode only takes overpotential of as low as ≈106 mV to deliver current density of 1000 mA cm-2, and maintains exceptional stability for over 1000 h in 1 m KOH. While in 0.5 m H2SO4, the Ru90Ni10/rGOP hybrid electrode exhibits acidic HER catalytic behavior comparable to commercially available Pt/C catalyst due to the formation of monometallic Ru shell. These electrochemical behaviors outperform some of the best Ru-based catalysts and make it attractive alternative to Pt-based catalysts toward highly efficient HER.
Aqueous zinc-ion batteries are attractive post-lithium battery technologies for grid-scale energy storage because of their inherent safety, low cost and high theoretical capacity. However, their practical implementation in wide-temperature surroundings persistently confronts irregular zinc electrodeposits and parasitic side reactions on metal anode, which leads to poor rechargeability, low Coulombic efficiency and short lifespan. Here, this work reports lamellar nanoporous Cu/Al2Cu heterostructure electrode as a promising anode host material to regulate high-efficiency and dendrite-free zinc electrodeposition and stripping for wide-temperatures aqueous zinc-ion batteries. In this unique electrode, the interconnective Cu/Al2Cu heterostructure ligaments not only facilitate fast electron transfer but work as highly zincophilic sites for zinc nucleation and deposition by virtue of local galvanic couples while the interpenetrative lamellar channels serving as mass transport pathways. As a result, it exhibits exceptional zinc plating/stripping behaviors in aqueous hybrid electrolyte of diethylene glycol dimethyl ether and zinc trifluoromethanesulfonate at wide temperatures ranging from 25 to -30 °C, with ultralow voltage polarizations at various current densities and ultralong lifespan of >4000 h. The outstanding electrochemical properties enlist full cell of zinc-ion batteries constructed with nanoporous Cu/Al2Cu and ZnxV2O5/C to maintain high capacity and excellent stability for >5000 cycles at 25 and -30 °C.
Metal-carbon composites are extensively utilized as electrochemical catalysts but face critical challenges in mass production and stability. We report a scalable manufacturing process for ruthenium surface-embedded fabric electrocatalysts (Ru-SFECs) via conventional fiber/fabric manufacturing. Ru-SFECs have excellent catalytic activity and stability toward the hydrogen evolution reaction, exhibiting a low overpotential of 11.9 mV at a current density of 10 mA cm-2 in an alkaline solution (1.0 M aq KOH solution) with only a slight overpotential increment (6.5%) after 10,000 cycles, whereas under identical conditions, that of commercial Pt/C increases 6-fold (from 1.3 to 7.8 mV). Using semipilot-scale equipment, a protocol is optimized for fabricating continuous self-supported electrocatalytic electrodes. Tailoring the fiber processing parameters (tension and temperature) can optimize the structural development, thereby achieving good catalytic performance and mechanical integrity. These findings underscore the significance of self-supporting catalysts, offering a general framework for stable, binder-free electrocatalytic electrode design.
Crafting single-atom catalysts (SACs) that possess "just right" modulated electronic and geometric structures, granting accessible active sites for direct room-temperature benzene oxidation is a coveted objective. However, achieving this goal remains a formidable challenge. Here, we introduce an innovative in situ phosphorus-immitting strategy using a new phosphorus source (phosphorus nitride, P3N5) to construct the phosphorus-rich copper (Cu) SACs, designated as Cu/NPC. These catalysts feature locally protruding metal sites on a nitrogen (N)-phosphorus (P)-carbon (C) support (NPC). Rigorous analyses, including X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS), validate the coordinated bonding of nitrogen and phosphorus with atomically dispersed Cu sites on NPC. Crucially, systematic first-principles calculations, coupled with the climbing image nudged-elastic-band (CI-NEB) method, provide a comprehensive understanding of the structure-property-activity relationship of the distorted Cu-N2P2 centers in Cu/NPC for selective oxidation of benzene to phenol production. Interestingly, Cu/NPC has shown more energetically favorable C-H bond activation compared to the benchmark Cu/NC SACs in the direct oxidation of benzene, resulting in outstanding benzene conversion (50.3 %) and phenol selectivity (99.3 %) at room temperature. Furthermore, Cu/NPC achieves a remarkable turnover frequency of 263â h-1 and mass-specific activity of 35.2â mmol g-1 h-1, surpassing the state-of-the-art benzene-to-phenol conversion catalysts to date.
Metallic zinc is a promising anode material for rechargeable aqueous multivalent metal-ion batteries due to its high capacity and low cost. However, the practical use is always beset by severe dendrite growth and parasitic side reactions occurring at anode/electrolyte interface. Here we demonstrate dynamic molecular interphases caused by trace dual electrolyte additives of D-mannose and sodium lignosulfonate for ultralong-lifespan and dendrite-free zinc anode. Triggered by plating and stripping electric fields, the D-mannose and lignosulfonate species are alternately and reversibly (de-)adsorbed on Zn metal, respectively, to accelerate Zn2+ transportation for uniform Zn nucleation and deposition and inhibit side reactions for high Coulombic efficiency. As a result, Zn anode in such dual-additive electrolyte exhibits highly reversible and dendrite-free Zn stripping/plating behaviors for >6400â hours at 1â mA cm-2, which enables long-term cycling stability of Zn||ZnxMnO2 full cell for more than 2000â cycles.
Ongoing research to develop advanced electrocatalysts for the oxygen evolution reaction (OER) is needed to address demand for efficient energy conversion and carbon-free energy sources. In the OER process, acidic electrolytes have higher proton concentration and faster response than alkaline ones, but their harsh strongly acidic environment requires catalysts with greater corrosion and oxidation resistance. At present, iridium oxide (IrO2 ) with its strong stability and excellent catalytic performance is the catalyst of choice for the anode side of commercial PEM electrolysis cells. However, the scarcity and high cost of iridium (Ir) and the unsatisfactory activity of IrO2 hinder industrial scale application and the sustainable development of acidic OER catalytic technology. This highlights the importance of further research on acidic Ir-based OER catalysts. In this review, recent advances in Ir-based acidic OER electrocatalysts are summarized, including fundamental understanding of the acidic OER mechanism, recent insights into the stability of acidic OER catalysts, highly efficient Ir-based electrocatalysts, and common strategies for optimizing Ir-based catalysts. The future challenges and prospects of developing highly effective Ir-based catalysts are also discussed.
Aqueous aluminum-ion batteries are attractive post-lithium battery technologies for large-scale energy storage in virtue of abundant and low-cost Al metal anode offering ultrahigh capacity via a three-electron redox reaction. However, state-of-the-art cathode materials are of low practical capacity, poor rate capability, and inadequate cycle life, substantially impeding their practical use. Here layered manganese oxide that is pre-intercalated with benzoquinone-coordinated aluminum ions (BQ-Alx MnO2 ) as a high-performance cathode material of rechargeable aqueous aluminum-ion batteries is reported. The coordination of benzoquinone with aluminum ions not only extends interlayer spacing of layered MnO2 framework but reduces the effective charge of trivalent aluminum ions to diminish their electrostatic interactions, substantially boosting intercalation/deintercalation kinetics of guest aluminum ions and improving structural reversibility and stability. When coupled with Zn50 Al50 alloy anode in 2 m Al(OTf)3 aqueous electrolyte, the BQ-Alx MnO2 exhibits superior rate capability and cycling stability. At 1 A g-1 , the specific capacity of BQ-Alx MnO2 reaches ≈300 mAh g-1 and retains ≈90% of the initial value for more than 800 cycles, along with the Coulombic efficiency of as high as ≈99%, outperforming the Alx MnO2 without BQ co-incorporation.
Efficient and stable catalysts are highly desired for the electrochemical conversion of hydrogen, oxygen, and water molecules, processes which are crucial for renewable energy conversion and storage technologies. Herein, we report the development of hollow nitrogenated carbon sphere (HNC) dispersed rhodium (Rh) single atoms (Rh1HNC) as an efficient catalyst for bifunctional catalysis. The Rh1HNC was achieved by anchoring Rh single atoms in the HNC matrix with an Rh-N3C1 configuration, via a combination of in situ polymerization and carbonization approach. Benefiting from the strong metal atom-support interaction (SMASI), the Rh and C atoms can collaborate to achieve robust electrochemical performance toward both the hydrogen evolution and oxygen reduction reactions in acidic media. This work not only provides an active site with favorable SMASI for bifunctional catalysis but also brings a strategy for the design and synthesis of efficient and stable bifunctional catalysts for diverse applications.
Hydrogen is a promising clean energy source, an alternative to fossil fuels, and can potentially play a crucial role in reducing carbon emissions. The transportation and storage of hydrogen are the biggest hurdles to realizing a hydrogen economy. Ammonia is considered to be one of the most promising hydrogen carriers, because of its high hydrogen content and easy liquefaction in mild conditions. To date, ammonia is mostly produced by the 'thermocatalytic' Haber-Bosch process, which requires high temperature and pressure. As a result, it can only produce ammonia in 'centralized' manufacturing systems. Mechanochemistry, a newly emerging method for efficient ammonia synthesis, offers potential advantages over the Haber-Bosch process. Mechanochemical ammonia synthesis under near ambient conditions can be connected with 'localized' sustainable energy systems. In this perspective, the state-of-the-art mechanochemical ammonia synthesis processes will be introduced. Challenges and opportunities are also discussed in relation to its role in a hydrogen economy.
Potassium oxide (K2O) is used as a promotor in industrial ammonia synthesis, although metallic potassium (K) is better in theory. The reason K2O is used is because metallic K, which volatilizes around 400 °C, separates from the catalyst in the harsh ammonia synthesis conditions of the Haber-Bosch process. To maximize the efficiency of ammonia synthesis, using metallic K with low temperature reaction below 400 °C is prerequisite. Here, we synthesize ammonia using metallic K and Fe as a catalyst via mechanochemical process near ambient conditions (45 °C, 1 bar). The final ammonia concentration reaches as high as 94.5 vol%, which was extraordinarily higher than that of the Haber-Bosch process (25.0 vol%, 450 °C, 200 bar) and our previous work (82.5 vol%, 45 °C, 1 bar).
Developing robust nonprecious-metal electrocatalysts with high activity towards sluggish oxygen-evolution reaction is paramount for large-scale hydrogen production via electrochemical water splitting. Here we report that self-supported laminate composite electrodes composed of alternating nanoporous bimetallic iron-cobalt alloy/oxyhydroxide and cerium oxynitride (FeCo/CeO2-xNx) heterolamellas hold great promise as highly efficient electrocatalysts for alkaline oxygen-evolution reaction. By virtue of three-dimensional nanoporous architecture to offer abundant and accessible electroactive CoFeOOH/CeO2-xNx heterostructure interfaces through facilitating electron transfer and mass transport, nanoporous FeCo/CeO2-xNx composite electrodes exhibit superior oxygen-evolution electrocatalysis in 1 M KOH, with ultralow Tafel slope of ~33 mV dec-1. At overpotential of as low as 360 mV, they reach >3900 mA cm-2 and retain exceptional stability at ~1900 mA cm-2 for >1000 h, outperforming commercial RuO2 and some representative oxygen-evolution-reaction catalysts recently reported. These electrochemical properties make them attractive candidates as oxygen-evolution-reaction electrocatalysts in electrolysis of water for large-scale hydrogen generation.
Single atom catalysts (SACs) with isolated active sites exhibit the highest reported mass activity for hydrogen evolution catalysis, which is crucial for practical applications. Here, we demonstrate that ultrahigh mass activity can also be achieved by rationally merging the isolated platinum (Pt) active sites in SAC. The catalyst was obtained by the thermodynamically driven diffusing and merging phosphorus-doped carbon (PC) supported Pt single atoms (Pt1@PC) into Pt nanoclusters (PtM@PC). X-ray absorption spectroscopy analysis revealed that the merged nanoclusters exhibit much stronger interactions with the support than the traditional method, enabling more efficient electron transfer. The optimized PtM@PC exhibited an order of magnitude higher mass activity (12.7 A mgPt-1) than Pt1@PC (0.9 A mgPt-1) at an overpotential of 10 mV in acidic media, which is the highest record to date, far exceeding reports for other outstanding SACs. Theoretical study revealed that the collective active sites in PtM@PC exhibit both favorable hydrogen binding energy and fast reaction kinetics, leading to the significantly enhanced mass activity. Despite its low Pt content (2.2 wt %), a low hydrogen production cost of â¼3 USD kg-1 was finally achieved in the full-water splitting at a laboratory scale.
Developing covalent organic frameworks (COFs) with good electrical conductivity is essential to widen their range of practical applications. Thermal annealing is known to be a facile approach for enhancing conductivity. However, at higher temperatures, most COFs undergo amorphization and/or thermal degradation because of the lack of linker rigidity and physicochemical stability. Here, we report the synthesis of a conductive benzoxazole-linked COF/carbon hybrid material (BCOF-600C) by simple thermal annealing. The fused-aromatic benzoxazole and biphenyl building units endow the resulting COF with excellent physicochemical stability against high temperatures and strong acids/bases. This allows heat treatment to further enhance electrical conductivity with minimal structural alteration. The robust crystalline structure with periodically incorporated nitrogen atoms allowed platinum (Pt) atoms to be atomically integrated into the channel walls of BCOF-600C. The resulting electrocatalyst with well-defined active sites exhibited superior catalytic performance toward hydrogen evolution in acidic media.
The oxygen reduction reaction is essential for fuel cells and metal-air batteries in renewable energy technologies. Developing platinum-group-metal (PGM)-free catalysts with comparable catalytic performance is highly desired for cost efficiency. Here, we report a tin (Sn) nanocluster confined catalyst for the electrochemical oxygen reduction. The catalyst was fabricated by confining 1-1.5 nm sized Sn nanoclusters in situ in microporous nitrogen-doped carbon polyhedra (SnxNC) with an average pore size of 0.7 nm. SnxNC exhibited high catalytic performance in acidic media, including positive onset and half-wave potentials, comparable to those of the state-of-the-art Pt/C and far exceeding those of the Sn single-atom catalyst. Combined structural and theoretical analyses reveal that the confined Sn nanoclusters, which have favorable oxygen adsorption behaviors, are responsible for the high catalytic performance, but not Sn single atoms.
After the emergence of graphene in the material science field, top-down and bottom-up studies to develop semiconducting organic materials with layered structures became highly active. However, most of them have suffered from poor processability, which hampers device fabrication and frustrates practical applications. Here, we suggest an unconventional approach to fabricating semiconducting devices, which avoids the processability issue. We designed a soluble amorphous network using a solution process to form a thin film on a substrate. We then employed heat treatment to develop a flattened organic structure in the thin film, as an active layer for organic thin-film transistors (TFTs). The fabricated TFTs showed good performance in both horizontal and vertical charge transport, suggesting a versatile and useful approach for the development of organic semiconductors.
Carbon hydrogasification is the slowest reaction among all carbon-involved small-molecule transformations. Here, we demonstrate a mechanochemical method that results in both a faster reaction rate and a new synthesis route. The reaction rate was dramatically enhanced by up to 4 orders of magnitude compared to the traditional thermal method. Simultaneously, the reaction exhibited very high selectivity (99.8 % CH4 , versus 80 % under thermal conditions) with a cobalt catalyst. Our study demonstrated that this extreme increase in reaction rate originates from the continuous activation of reactive carbon species via mechanochemistry. The high selectivity is intimately related to the activation at low temperature, at which higher hydrocarbons are difficult to form. This work is expected to advance studies of carbon hydrogasification, and other solid-gas reactions.
Single-atom catalysts have recently attracted considerable attention because of their highly efficient metal utilization and unique properties. Finding a green, facile method to synthesize them is key to their widespread commercialization. Here we show that single-atom catalysts (including iron, cobalt, nickel and copper) can be prepared via a top-down abrasion method, in which the bulk metal is directly atomized onto different supports, such as carbon frameworks, oxides and nitrides. The level of metal loading can be easily tuned by changing the abrasion rate. No synthetic chemicals, solvents or even water were used in the process and no by-products or waste were generated. The underlying reaction mechanism involves the mechanochemical force in situ generating defects on the supports, then trapping and stably sequestering atomized metals.
The catalytic conversion of energy-related small-molecules is a critical process in the fields of chemical production, environmental restoration, and energy conversion and storage. Over the years, numerous nanocatalytic materials have been explored in efforts to substantially boost the inherently sluggish catalytic processes. Despite achievements, the lack of fundamental insights into the design and identification of active sites and the structure-performance relationship has been one of the main obstacles to further improvement in catalytic performance. With the development of first-principles density functional theory (DFT) calculations and state-of-art spectroscopic techniques, the pace of research has started to move forward again.In this Account, we illustrate our recent representative attempts to gain fundamental insights into the rational development of efficient nanocatalytic materials and thus boost the typical electrochemical and mechanochemical conversions of energy-related small-molecules, including for the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and ammonia synthesis. DFT calculations and advanced spectroscopic techniques, such as synchrotron radiation-based X-ray absorption spectroscopy (XAS, hard and soft X-ray), were properly adopted for this purpose.Specifically, to achieve a fast-electrochemical hydrogen evolution process, Ir active sites with balanced hydrogen adsorption/desorption behaviors were first computationally designed via orbital modulation and experimentally identified, and they showed significantly enhanced catalytic activity toward HER in acidic media. For the electrochemical reduction of oxygen, well-designed Zn-N2 active sites and quinone functional groups were introduced into the different carbon matrixes and structurally identified by the XAS technique, utilizing hard and soft X-rays, respectively. Both experimental and DFT studies revealed that Zn-N2 active sites with their unique structure can greatly activate the adsorbed oxygen species, leading to a highly efficient and selective four-electron oxygen reduction pathway, while the quinone functional groups are able to modify the activation mode and alter it into a selective two-electron oxygen reduction pathway for H2O2 production.In another study, inspired by the dissociation of stable nitrogen molecules on the surface of Fe, dynamic strained Fe active sites were designed for mechanochemical ammonia synthesis. Combined XAS and Mössbauer spectroscopy revealed the formation of a short-range Fe4N structure by the Fe active sites and dissociated nitrogen during the ball milling process, facilitating robust hydrogenation and ammonia production under mild conditions.Thanks to the theoretical methods and advanced spectroscopic techniques, fundamental insights into the design and identification of active sites and understanding of the structure-performance relationship can be easily obtained using such tools, which will guide the development of nanocatalytic materials and boost the conversions of energy-related small-molecules for various applications.
Hydrogen peroxide (H2 O2 ) is an environment-friendly and efficient oxidant with a wide range of applications in different industries. Recently, the production of hydrogen peroxide through direct electrosynthesis has attracted widespread research attention, and has emerged as the most promising method to replace the traditional energy-intensive multi-step anthraquinone process. In ongoing efforts to achieve highly efficient large-scale electrosynthesis of H2 O2 , carbon-based materials have been developed as 2e- oxygen reduction reaction catalysts, with the benefits of low cost, abundant availability, and optimal performance. This review comprehensively introduces the strategies for optimizing carbon-based materials toward H2 O2 production, and the latest advances in carbon-based hybrid catalysts. The active sites of the carbon-based materials and the influence of coordination heteroatom doping on the selectivity of H2 O2 are extensively analyzed. In particular, the appropriate design of functional groups and understanding the effect of the electrolyte pH are expected to further improve the selective efficiency of producing H2 O2 via the oxygen reduction reaction. Methods for improving catalytic activity by interface engineering and reaction kinetics are summarized. Finally, the challenges carbon-based catalysts face before they can be employed for commercial-scale H2 O2 production are identified, and prospects for designing novel electrochemical reactors are proposed.
Oxygen evolution catalysis plays a crucial role in the solar-to-fuel conversion for green energy applications. However, developing efficient and stable catalysts for the oxygen evolution catalysis remains a great challenge. Here, we successfully activate an inefficient oxygen evolution catalyst using a simple single atom tailoring strategy. The Rh element with its unfilled 4d8 electron configuration was selected to atomically implant into a Cu oxide matrix, which has a filled 3d10 electron configuration. The hetero-Rh single atom (SA) migration was achieved by dispersing Cu2O nanocubes in a RhCl3 aqueous solution, enabling an ion exchange process. The activated catalyst (Cu2O-RhSA) exhibited significantly enhanced catalytic activity toward oxygen evolution in alkaline media, surpassing the performance of pristine Cu2O nanocubes and commercial IrO2. A theoretical study further confirmed that the migrated hetero-Rh SAs can tailor the interaction between the Cu and O sites, modulating the electron density distribution on the surface of Cu2O, leading to a more favorable oxygen evolution process.
