Single-Walled Carbon Nanotube Induced Optimized Electron Polarization of Rhodium Nanocrystals To Develop an Interface Catalyst for Highly Efficient Electrocatalysis

Enhanced Alkaline Hydrogen Evolution Reaction via Electronic Structure Regulation: Activating PtRh with Rare Earth Tm Alloying

Developing high-performance electrocatalysts for alkaline hydrogen evolution reaction (HER) is crucial for producing green hydrogen, yet it remains challenging due to the sluggish kinetics in alkaline environments. Pt is located near the peak of HER volcano plot, owing to its exceptional performance in hydrogen adsorption and desorption, and Rh plays an important role in H2O dissociation. Lanthanides (Ln) are commonly used to modulate the electronic structure of materials and further influence the adsorption/desorption of reactants, intermediates, and products, and noble metal-Ln alloys are recognized as effective platforms where Ln elements regulate the catalytic properties of noble metals. Here Pt1.5Rh1.5Tm alloy is synthesized using the sodium vapor reduction method. This alloy demonstrates superior catalytic activity, being 4.4 and 6.6 times more effective than Pt/C and Rh/C, respectively. Density Functional Theory (DFT) calculations reveal that the upshift of d-band center and the charge transfer induced by alloying promote adsorption and dissociation of H2O, making Pt1.5Rh1.5Tm alloy more favorable for the alkaline HER reaction, both kinetically and thermodynamically.

Establishing Ohmic Contact of a Radial Compressed CNT Bundle with High Work Function Metal

Establishing low-resistance ohmic contact is critical for developing electronic devices based on traditional silicon and new low-dimensional materials. Due to unprecedented electronic and mechanical properties, the one-dimensional carbon nanotubes (CNTs) have been used as source/drain, gate, or tunnel to fabricate transistors. However, the mechanism causing low-resistance ohmic contact is not clear yet. Here, the hybrid atomic force microscopy-scanning electron microscopy (AFM-SEM) instrument was developed to establish lower-resistance ohmic contact between a radial compressed deformed multiwalled CNT bundle and high work function metal (platinum and gold). The radial compression structure under strong van der Waals attraction was in situ characterized through the SEM image to obtain the diameter and width and through AFM to get height and to perform nanoindentation, indicating that Pt has the smaller radial compression deformation. Molecular dynamics simulations exhibit that compared to Pt, a wider ribbon-like graphene layer formed when the radial compressed CNTs contacted with Au. The bond forming and electron orbital overlapping between C atoms of deformed CNTs and the high work function metal atom is beneficial for good electrical contact.

Enhanced Alkaline Hydrogen Evolution Reaction through Lanthanide-Modified Rhodium Intermetallic Catalysts

Design of highly efficient electrocatalysts for alkaline hydrogen evolution reaction (HER) is of paramount importance for water electrolysis, but still a considerable challenge because of the slow HER kinetics in alkaline environments. Alloying is recognized as an effective strategy to enhance the catalytic properties. Lanthanides (Ln) are recognized as an electronic and structural regulator, attributed to their unique 4f electron behavior and the phenomenon known as lanthanide contraction. Here, a new class of Rh3Ln intermetallics (IMs) are synthesized using the sodium vapor reduction method. The alloying process induced an upshift of the d-band center and electron transfer from Ln to Rh, resulting in optimized adsorption and dissociation energies for H2O molecules. Consequently, Rh3Tb IMs exhibited outstanding HER activity in both alkaline environments and seawater, displaying an overpotential of only 19 mV at 10 mA cm-2 and a Tafel slope of 22.2 mV dec-1. Remarkably, the current density of Rh3Tb IMs at 100 mV overpotential is 8.6 and 5.7 times higher than that of Rh/C and commercial Pt/C, respectively. This work introduces a novel approach to the rational design of HER electrocatalysis and sheds light on the role of lanthanides in electrocatalyst systems.

Substrate Strain Engineering of Single-Atomic Sn-N4 Sites Embedded in Various Carbon Matrixes for Bifunctional Oxygen Electrocatalysis

It is still a great challenge to design and synthesize high-efficiency and low-cost single-atom catalysts (SACs) as promising bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Herein, theoretical insights into Sn-N₄ embedded carbon nanotubes, graphene quantum dots, and graphene nanosheets (denoted as Sn-N₄-CNTs, Sn-N₄-GQDs, and Sn-N₄-Gra, respectively) for the ORR/OER are systematically provided. These results show that the protruding Sn atom creates a Sn-N₄ pyramid and induces varied strain transfer between Sn-N₄ and different carbon substrates prior to adsorption of O intermediates, resulting in the opposite response of the adsorption strengths of O intermediates to the substrate curvature of Sn-N₄-CNTs and Sn-N₄-GQDs. The torsional strain induced by OH* and OOH* on the Sn atom of Sn-N₄-CNTs breaks the scaling relations between the adsorption strengths of O intermediates. Consequently, Sn-N₄-CNTs with suitable curvature achieve outstanding ORR performance with very low overpotentials (0.28 V). Furthermore, the increase of curvature boosts the OER activity of Sn-N₄-CNTs. For Sn-N₄-GQDs, high curvature contributes to promoted OER activity but reduced ORR activity. The electronic interactions reveal the electron transfer from the s/p-bands of Sn to the half-filled β states of the frontier orbitals of O intermediates.

Atomically Dispersed MoOx on Rhodium Metallene Boosts Electrocatalyzed Alkaline Hydrogen Evolution

Accelerating slow water dissociation kinetics is key to boosting the hydrogen evolution reaction (HER) in alkaline media. We report the synthesis of atomically dispersed MoO_x species anchored on Rh metallene using a one-pot solvothermal method. The resulting structures expose the oxide-metal interfaces to the maximum extent. This leads to a MoO_x -Rh catalyst with ultrahigh alkaline HER activity. We obtained a mass activity of 2.32 A mg_Rh ^-1 at an overpotential of 50 mV, which is 11.8 times higher than that of commercial Pt/C and surpasses the previously reported Rh-based electrocatalysts. First-principles calculations demonstrate that the interface between MoO_x and Rh is the active center for alkaline HER. The MoO_x sites preferentially adsorb and dissociate water molecules, and adjacent Rh sites adsorb the generated atomic hydrogen for efficient H₂ evolution. Our findings illustrate the potential of atomic interface engineering strategies in electrocatalysis.

Asymmetric Activation of the Nitro Group over a Ag/Graphene Heterointerface to Boost Highly Selective Electrocatalytic Reduction of Nitrobenzene

The electrocatalytic reduction of nitrobenzene to aniline normally faces high overpotential and poor selectivity because of its six-electron redox nature. Herein, a Ag nanoparticles/laser-induced-graphene (LIG) heterointerface was fabricated on polyimide films and employed as an electrode material for an efficient nitrobenzene reduction reaction (NBRR) via a one-step laser direct writing technology. The first-principles calculations reveal that Ag/LIG shows the lowest activation barriers for the NBRR, which could be attributed to the optimum adsorption of the H atom realized by the appropriate interaction between Ag/LIG heterointerfaces and nitrobenzene. As a result, the overpotential of the NBRR is reduced by 217 mV after silver loading, and Ag/LIG shows a high aniline selectivity of 93%. Furthermore, an electrochemical reduction of nitrobenzene in tandem with an electrochemical oxidative polymerization of aniline was designed to serve as an alternative method to remove nitrobenzene from the aqueous solution. This strategy highlights the significance of heterointerfaces for efficient electrocatalysts, which may stimulate the development of novel electrocatalysts to boost the electrocatalytic activity.

Single-Step and Room-Temperature Synthesis of Laser-Induced Pt/VC Nanocomposites as Effective Bifunctional Electrocatalysts for Hydrogen Evolution and Oxygen Evolution Reactions

The development of cost-effective Pt-based electrocatalysts is of great scientific and industrial significance for improving the electrocatalytic activity of hydrogen evolution (HER) and oxygen evolution (OER) reactions for overall water splitting. In this work, unlike traditional furnace pyrolysis, we report the rapid and single-step room-temperature synthesis of Pt/VC nanocomposites with a three-dimensional (3D) network porous structure by laser irradiation technology. The resultant Pt-based composite (Pt/VC-2.84) could be applied to HER under different pH conditions. In particular, the content of Pt in Pt/VC-2.84 is only 2.84 wt %, which is far lower than that in the advanced HER electrocatalyst with the Pt content of 20 wt % (commercial 20 wt % Pt/C). In addition, Pt/VC-2.84 exhibits a boosted higher OER activity and stability than RuO2 in an alkaline medium. Most importantly, electrocatalytic results reflect that Pt/VC-2.84 reveals superior activity and stability toward overall water splitting.

Controlling the Interfacial Charge Polarization of MOF-Derived 0D-2D vdW Architectures as a Unique Strategy for Bifunctional Oxygen Electrocatalysis

The design of alternative earth-abundant van der Waals (vdW) nanoheterostructures for bifunctional oxygen evolution/reduction (OER/ORR) electrocatalysis is of paramount importance to fabricate energy-related devices. Herein, we report a simple metal-organic framework (MOF)-derived synthetic strategy to fabricate low-dimensional (LD) nanohybrids formed by zero-dimensional (0D) ZrO₂ nanoparticles (NPs) and heteroatom-doped two-dimensional (2D) carbon nanostructures. The 2D platforms controlled the electronic structures of interfacial Zr atoms, thus producing optimized electron polarization for boron and nitrogen-doped carbon (BCN)/ZrO₂ nanohybrids. X-ray photoelectron spectroscopy (XPS) and theoretical studies revealed the key role of the synergistic couple effect of boron (B) and nitrogen (N) in interfacial electronic polarization. The BCN/ZrO₂ nanohybrid showed excellent bifunctional electrocatalytic activity, delivering an overpotential (η₁₀) of 301 mV to reach a current density of 10 mA-cm^-2 for the OER process and a half-wave potential (E_1/2) of 0.85 V vs reversible hydrogen electrode (RHE) for the ORR process, which are comparable to the state-of-the-art LD nanohybrids. Furthermore, BCN/ZrO₂ also showed competitive performances for water-splitting and zinc-air battery devices. This work establishes a new route to fabricate highly efficient multifunctional electrocatalysts by tuning the electronic polarization properties of 0D-2D electrochemical interfaces.

Plasma-assisted rhodium incorporation in nickel–iron sulfide nanosheets: enhanced catalytic activity and the Janus mechanism for overall water splitting

Rh was incorporated in Fe-doped Ni3S2 nanosheets with the assistance of hydrogen plasma to significantly enhance the HER/OER catalytic activity. The operando evolution behavior and Janus catalytic mechanism of this catalyst were further revealed.

Sulfur doped ruthenium nanoparticles as a highly efficient electrocatalyst for the hydrogen evolution reaction in alkaline media

Sulfur-doped ruthenium ultrafine nanoparticles is obtained via a simple solvothermal procedure, which shows excellent hydrogen evolution performance in alkaline media.

Carbon supported noble metal nanoparticles as efficient catalysts for electrochemical water splitting

Due to an increasing requirement of clean and sustainable hydrogen energy economy, it is significant to develop new highly effective catalysts for electrochemical water splitting. In alkaline electrolyte, Platinum (Pt) shows a much slower hydrogen evolution reaction (HER) kinetics relative to acidic condition. Here, we show a versatile synthetic approach for combining different noble metals, such as Rhodium (Rh), RhPt and Pt nanoparticles, with carbon forming noble metal nanoparticles/nanocarbon composites, denoted as Rh(nP)/nC, RhPt(nP)/nC and Pt(nP)/nC, respectively. It was found that in alkaline media these composites exhibited higher performance for the HER than the commercial Pt/C. In particular, Rh(nP)/nC displayed a small overpotential of 44 mV at a current density of 5 mA cm-2 and a low Tafel slope of 50 mV dec-1. Meanwhile, it also showed a comparable activity for the oxygen evolution reaction (OER) to the benchmarking catalyst RuO2. The superior HER and OER performance benefits from the very small size of nanoparticles and synergy between carbon support and nanoparticles.

Rhodium/graphitic-carbon-nitride composite electrocatalyst facilitates efficient hydrogen evolution in acidic and alkaline electrolytes

Exploring the highly efficient and durable electrocatalysts for hydrogen evolution reaction (HER) is vitally necessary for sustainable energy conversion and storage system. Herein, we fabricate an interfacial engineered Rh-carbon nitride as advanced electrocatalysts for HER in the acidic and alkaline electrolytes. The interface between Rh nanocrystals and carbon nitride may adjust the electronic structure of Rh, which results in high activity for HER. The optimal Rh-carbon nitride shows low overpotential at current density of -10 mA·cm^-2 and small Tafel slope (13 mV and 25.0 mV dec^-1 in 0.5 M H₂SO₄, 46 mV and 42.0 mV dec^-1 in 1.0 M KOH, respectively), which is superior to that of commercial Pt/C (21 mV and 28.5 mV dec^-1 in 0.5 M H₂SO₄, 55 mV and 44.0 mV dec^-1 in 1.0 M KOH, respectively). Importantly, this composite also exhibits long-term stability in 0.5 M H₂SO₄ and 1.0 M KOH. The excellent HER performances can be attribute to the interface between Rh and carbon nitride, which downshifts their d-band center positions, tuning the adsorption ability for hydrogen and accelerating the HER kinetics. This work may open up an efficient method to design metal/carbon hybrid for electrocatalysis.

Electronic Asymmetric Distribution of RhCu Bimetallic Nanocrystals for Enhancing Trifunctional Electrocatalysis

Developing efficient and durable multifunctional electrocatalysts for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR) is of significant importance for many electrochemical energy devices, such as water electrolyzers, metal-air batteries, and fuel cells. Herein, the Rh-Cu alloy nanocrystals (NCs) are prepared with a simple wet-chemical approach. The tuning of morphology and the asymmetric electron distribution provide more efficient Rh-Cu bimetallic sites. Meanwhile, the incorporation of Cu into the Rh lattice could reduce the oxidation of Rh-Cu bimetallic sites and increase the catalytic stability. Under the tuning of the composition, the drastically enhanced electrocatalytic activities of HER, OER, and ORR are achieved in the Rh₆Cu₁ NCs with the cell voltage required to be as low as 1.55 V to accomplish an overall water splitting of 10 mA cm^-2 and a maximum power density of 142.58 mW cm^-2 for a zinc-air battery with good stability, representing the best trifunctional electrocatalysts for all we know. This work highlights the design and control of Rh-Cu NCs, which could be a potential alternative approach to trifunctional catalysis and further boosts the development of the bimetallic electrocatalysts in the energy conversion system.

Direct Hybridization of Noble Metal Nanostructures on 2D Metal-Organic Framework Nanosheets To Catalyze Hydrogen Evolution

Rational hybridization of two-dimensional (2D) nanomaterials with extrinsic species has shown great promise for a wide range of applications. To date, rational design and engineering of heterostructures based on 2D metal-organic frameworks (MOFs) has been rather limited. Herein, we report an efficient strategy to construct noble metal/2D MOF heterostructures, featuring the utilization of surface oxygen sites from uncoordinated MOF ligands. The incorporation of highly dispersed noble metal nanoparticles (e.g., Pt and Pd) with modulated electronic structure is enabled on a surfactant-free MOF surface. As a proof-of-concept demonstration, the 2D Ni-MOF@Pt hybrid with well-defined interfaces is applied to boost the electrochemical hydrogen evolution reaction (HER) and delivers decent electrocatalytic activity under both acidic and alkaline conditions. The present results are expected to provide new insights into furnishing MOFs with extended functionalities and applications.

0.2 V Electrolysis Voltage-Driven Alkaline Hydrogen Production with Nitrogen-Doped Carbon Nanobowl-Supported Ultrafine Rh Nanoparticles of 1.4 nm

The development of highly effective and low-cost electrocatalysts for energy-saving hydrogen production via water splitting is still a great challenge. Herein, porous nitrogen-doped carbon nanobowls (N-CBs) have been designed and used for the controlled growth of ultrafine rhodium (Rh) nanoparticles. With the aid of interfacial bonding of Rh and N, ultrafine Rh nanoparticles with an average size of 1.4 nm have been successfully immobilized on the N-CBs. This Rh/N-CB electrocatalyst shows superior activity and high stability for the hydrogen evolution reaction (HER) and the hydrazine oxidation reaction (HzOR). More importantly, the Rh/N-CBs exhibit high activity for hydrogen production from water electrolysis, marking with a cell voltage of 0.2 V to achieve a current density of 20 mA cm^-2 when they serve as cathodic electrocatalysts for the HER and anodic electrocatalysts for the HzOR in 1 M KOH with 0.5 M hydrazine. The density functional theory calculations demonstrate that a near-zero hydrogen adsorption free energy produced by the chemical bonding of Rh with the pyrrole-N doped in N-CBs is responsible for the excellent HER activity of Rh/N-CBs electrocatalysts.

Confining Pd Nanoparticles and Atomically Dispersed Pd into Defective MoO3 Nanosheet for Enhancing Electro- and Photocatalytic Hydrogen Evolution Performances

Interface engineering of two-dimensional (2D) transition-metal composites for activating plane and edge sites is a significant yet step challenging in boosting their performance for hydrogen evolution reaction (HER). Herein, two-dimensional (2D) MoO₃ with petal-shaped nanosheets confining Pd nanoparticles (Pd@MoO₃ heterostructure) was prepared via an efficient solvothermal and subsequently hydrogen reduction processes. The atomically dispersed Pd-substituted sites in the interface of Pd nanoparticles and 2D MoO₃ lattices significantly play an important role in enhancing the electrocatalytic and photocatalytic performances of the Pd@MoO₃ heterostructure. As a result, the Pd@MoO₃ heterostructure exhibits a high HER catalytic activity with an overpotential (η) of 71 mV to achieve a current density of 10 mA cm^-2 and an extremely low Tafel slope of 42.8 mV dec^-1 in 0.5 M H₂SO₄ solution. Furthermore, the photoresponse of the Pd@MoO₃ heterostructure is about 3 times higher than that of the MoO₃ nanosheets. This work highlighted a strategy of interface engineering for highly efficient cost-effective catalyst for hydrogen evolution by electric and solar energy conversion.

Robust noble metal-based electrocatalysts for oxygen evolution reaction

The oxygen evolution reaction (OER) is a kinetically sluggish anodic reaction and requires a large overpotential to deliver appreciable current. Despite the fact that non-precious metal-based alkaline water electrocatalysts are receiving increased attention, noble metal-based electrocatalysts (NMEs) applied in proton exchange membrane water electrolyzers still have advantageous features of larger current and power densities with lower stack cost. Engineering NMEs for OER catalysis with high efficiency, durability and utilization rate is of vital importance in promoting the development of cost-effective renewable energy production and conversion devices. In this tutorial review, we covered the recent progress in the composition and structure optimization of NMEs for OER including Ir- and Ru-based oxides and alloys, and noble-metals beyond Ir and Ru with a variety of morphologies. To shed light on the fundamental science and mechanisms behind composition/structure-performance relationships and activity-stability relationships, integrated experimental and theoretical studies were pursued for illuminating the metal-support interaction, size effect, heteroatom doping effect, phase transformation, degradation processes and single-atom catalysis. Finally, the challenges and outlook are provided for guiding the rational engineering of OER electrocatalysts for applications in renewable energy-related devices.