New Class Of Electrocatalysts Research Articles

Bamboo-Like Carbon Nanotube-Encapsulated Fe2C Nanoparticles Activate Confined Fe2O3 Nanoclusters Via d-p-d Orbital Coupling for Alkaline Oxygen Evolution Reaction.

The efficient anion exchange membrane water electrolysis is challenging with low cell voltage and long-term stability at large current density, due to the unstable anodic oxygen evolution reaction (OER). Fe-based electrocatalysts are potential candidates for the anodic OER. In Fe-based materials, iron oxides always show better stability in alkaline solution but lower OER activity. However, the catalysts in previous study are difficult to continuously and effectively activate iron oxides supported on carbon during electrocatalysis. Herein, a new class of electrocatalyst: bamboo-like carbon nanotubes (B-CNT)-encapsulated Fe2C nanoparticles (NPs) supported Fe2O3 nanoclusters (NCs), named Fe2O3/B-CNT@Fe2C is reported. Theoretical calculations and experimental results reveal that B-CNT-encapsulate Fe2C NPs activate Fe2O3 NCs by the d-p-d orbital coupling, thereby weakening the adsorption of OOH* intermediate during OER process. The electrolyzer based on the electrocatalyst requires only 1.48 V to reach 1.0 A cm-2 and shows a long-term stability at 1.0 A cm-2 for 1600 h, comparable to the best-reported values for the anion exchange membrane water electrolyzer (AEMWE).

Efficient Electrocatalysts for Alkaline Oxygen Evolution Reaction from Wolframite Derived Heteroatom Materials

AbstractNew materials for oxygen evolution reaction (OER) electrocatalysts in alkaline conditions have been highly investigated in recent years for the advancement of water splitting. However, questions such as the lack of stability and the use of noble metals as electrocatalysts still need to be addressed. In this study, we report the synthesis and electrocatalytic properties of a series of wolframite tungsten‐based materials (MWO4, M=Fe, Mn, Ni, Co) towards OER in basic conditions. Our results showed that Ni0.5Mn0.5WO4 is a promising electrocatalyst, exhibiting ease of preparation, stability over the course of our experiments, and OER activity comparable to the standard iridium oxide. This study highlights the potential of wolframite tungsten‐based materials as a new class of electrocatalysts for OER in alkaline conditions.

Interfacial Polarization Triggered by Covalent‐Bonded MXene and Black Phosphorus for Enhanced Electrochemical Nitrate to Ammonia Conversion

AbstractMXenes have recently emerged as a new class of electrocatalysts for diverse energy conversion reactions, but they are generally considered to be catalytically inert. Herein, a strategy of interfacial polarization is put forward to improve the catalytic activity of MXenes, with the construction of an interfacial structure consisting of black phosphorus (BP) nanoflakes and Nb2C MXene nanosheets for electrochemical nitrate reduction to ammonia as a proof of concept. The experimental and computational results reveal that a strong interfacial polarization is built between BP nanoflakes and Nb2C nanosheets in the prepared BP/Nb2C composite. The polarization of Nb centers by adjacent BP sites gives rise to the formation of positively centered Nb atoms and BP‐polarized Nb atoms, which synergistically catalyze the cleavage of N–O bonds in HNO2* to form NO*. In addition, the stabilization of monatomic *N by the BP/Nb2C composite is also enhanced compared with BP nanoflakes and Nb2C nanosheets. As a result, both the ammonia yield rate and Faraday efficiency of the BP/Nb2C composite are much higher than that of BP nanoflakes and Nb2C nanosheets. Overall, this work shows the great potential for constructing a strong interfacial polarization to improve the catalytic performance of MXenes‐based electrocatalysts.

The Weyl Semimetals MIrTe4 (M = Nb, Ta) as Efficient Catalysts for Dye‐Sensitized Hydrogen Evolution

AbstractThe prevalent global energy crisis calls for searching viable pathways for generating green hydrogen as an alternative energy resource. Dye‐sensitized photocatalytic water splitting is a feasible solution to produce green hydrogen. However, identifying suitable catalysts has been one of the bottlenecks in driving dye‐sensitized photocatalysis efficiently. In this work, a new class of electrocatalysts is reported based on the layered Weyl semimetals MIrTe4 (M = Nb, Ta) for the Eosin Y (EY)‐sensitized hydrogen evolution reaction (HER). NbIrTe4 and TaIrTe4 exhibit HER activities of ≈18 000 and 14 000 µmol g−1 respectively, after 10 h of irradiation with visible light. Time‐dependent UV‐Vis spectroscopy and high‐pressure liquid chromatography coupled with mass spectrometry analysis shed light on the reaction dynamics and enable a deeper understanding of the observed trend in hydrogen evolution rates for MIrTe4. MIrTe4 semimetals outperform transition metal‐based Weyl semimetals in terms of catalytic HER activity using EY as photosensitizer and triethanolamine as the sacrificial agent. It is hypothesized that the topology‐related band inversion in MIrTe4 Weyl semimetals promotes a high density of M d‐states near the Fermi level, driving their high catalytic performance. This study introduces a new class of layered Weyl semimetals as efficient catalysts, and provides perspectives for designing topology‐enhanced catalysts.

Paradigm in single-atom electrocatalysts for dinitrogen reduction to ammonia

Single-atom catalysts (SACs) are a new class of electrocatalysts for the electrochemical nitrogen reduction reaction.

The Native Oxide Skin of Liquid Metal Ga Nanoparticles Prevents Their Rapid Coalescence during Electrocatalysis.

Liquid metals (LMs) have been used in electrochemistry since the 19th century, but it is only recently that they have emerged as electrocatalysts with unique properties, such as inherent resistance to coke poisoning, which derives from the dynamic nature of their surface. The use of LM nanoparticles (NPs) as electrocatalysts is highly desirable to enhance any surface-related phenomena. However, LM NPs are expected to rapidly coalesce, similarly to liquid drops, which makes their implementation in electrocatalysis hard to envision. Herein, we demonstrate that liquid Ga NPs (18 nm, 26 nm, 39 nm) drive the electrochemical CO2 reduction reaction (CO2RR) while remaining well-separated from each other. CO is generated with a maximum faradaic efficiency of around 30% at -0.7 VRHE, which is similar to that of bulk Ga. The combination of electrochemical, microscopic, and spectroscopic techniques, including operando X-ray absorption, indicates that the native oxide skin of the Ga NPs is still present during CO2RR and provides a barrier to coalescence during operation. This discovery provides an avenue for future development of Ga-based LM NPs as a new class of electrocatalysts.

Unveiling the underlying mechanism of nitrogen fixation by a new class of electrocatalysts two-dimensional TM@g-C4N3 monosheets

The potential of TM atoms embedded g-C4N3 as a new class of electrocatalysts (TM@g-C4N3, TM = 3d, 4d and 5d transition metal) towards nitrogen reduction reaction (NRR) were systematically investigated through the combination of high-throughput screening and first-principles calculations. Among 30 candidate materials, TM@g-C4N3 (TM = V, Tc, Os, Pt) exhibited the highest activity for electrocatalytic N2 reduction to produce NH3. Particularly, V@g-C4N3 is identified as the most active catalyst for NRR with onset potential of −0.37 V. Interestingly, a volcano curve between Uonset (onset potential) and ΔEads(*N2) (the adsorption energy of N2) is established, and thus ΔEads(*N2) can be used as a descriptor to characterize the activity of catalysts. Among all investigated catalysts, the lowest onset potential of V@g-C4N3 can be attributed to its moderate adsorption energies for N2. After in-deep analysis of the intrinsic properties of the four catalysts, we found that the increasing order of catalytic activity is consistent with the increasing order of d-band center (εd) of the four catalysts. In addition, the excellent thermal stability of the four catalysts is verified via simulated annealing at 500 K for 10 ps. Furthermore, three catalysts TM@g-C4N3 (TM = V, Tc, Pt) demonstrate good selectivity. Therefore, V@g-C4N3 is a promising electrocatalyst for NRR. Our work opens the way for g-C4N3 as a new type of support to construct efficient single-atom catalyst for electrocatalytic ammonia synthesis. The predicted TM@g-C4N3 catalysts will provide useful guidance for experimental synthesis and rational design of catalysts in future.

Searching novel complex solid solution electrocatalysts in unconventional element combinations

Despite outstanding accomplishments in catalyst discovery, finding new, more efficient, environmentally neutral, and noble metal-free catalysts remains challenging and unsolved. Recently, complex solid solutions consisting of at least five different elements and often named as high-entropy alloys have emerged as a new class of electrocatalysts for a variety of reactions. The multicomponent combinations of elements facilitate tuning of active sites and catalytic properties. Predicting optimal catalyst composition remains difficult, making testing of a very high number of them indispensable. We present the high-throughput screening of the electrochemical activity of thin film material libraries prepared by combinatorial co-sputtering of metals which are commonly used in catalysis (Pd, Cu, Ni) combined with metals which are not commonly used in catalysis (Ti, Hf, Zr). Introducing unusual elements in the search space allows discovery of catalytic activity for hitherto unknown compositions. Material libraries with very similar composition spreads can show different activities vs. composition trends for different reactions. In order to address the inherent challenge of the huge combinatorial material space and the inability to predict active electrocatalyst compositions, we developed a high-throughput process based on co-sputtered material libraries, and performed high-throughput characterization using energy dispersive X-ray spectroscopy (EDS), scanning transmission electron microscopy (SEM), X-ray diffraction (XRD) and conductivity measurements followed by electrochemical screening by means of a scanning droplet cell. The results show surprising material compositions with increased activity for the oxygen reduction reaction and the hydrogen evolution reaction. Such data are important input data for future data-driven materials prediction.

Hierarchically Ordinated Two-Dimensional MoS2 Nanosheets on Three-Dimensional Reduced Graphene Oxide Aerogels as Highly Active and Stable Catalysts for Hydrogen Evolution Reaction

Hydrogen gas (H2) is being intensively proposed as a next-generation clean energy owing to the depletion of fossil fuels. Electrochemical water splitting is one of the most promising processes for hydrogen production. Furthermore, many efforts focusing on electrochemical water splitting have been made to develop low-cost, electrochemically active, and stable catalysts for efficient hydrogen production. MoS2 has emerged as an attractive material for developing catalysts for the hydrogen evolution reaction (HER). Hence, in this study, we design hierarchically ordinated two-dimensional (2D) MoS2 nanosheets on three-dimensional (3D) reduced graphene oxide (rGO) (H-2D/3D-MoS2-rGO) aerogel structures as a new class of electrocatalysts for the HER. We use the one-pot hydrothermal synthesis route for developing high-performance electroactive materials for the HER. The as-prepared H-2D/3D-MoS2-rGO contains a unique 3D hierarchical structure providing large surface areas owing to the 3D porous networks of rGO and more active sites owing to the many edge sites in the MoS2 nanosheets. In addition, the H-2D/3D-MoS2-rGO structure exhibits remarkable electrochemical properties during the HER. It shows a lower overpotential than pure MoS2 and excellent electrochemical stability owing to the large number of active sites (highly exposed edge sites) and high electrical conductivity from the rGO structure.

Discovery and Facile Synthesis of a New Silicon Based Family as Efficient Hydrogen Evolution Reaction Catalysts: A Computational and Experimental Investigation of Metal Monosilicides.

A new family of transition-metal monosilicides (MSi, M = Ti, Mn, Fe, Ru, Ni, Pd, Co, and Rh) electrocatalysts with superior electrocatalytic performance of hydrogen evolution is reported, based on the computational and experimental results. It is proposed that these MSi can be synthesized within several minutes by adopting the arc-melting method. The previously reported RuSi is not only fabricated more readily but eventually explored 8 MSi that can be good hydrogen evolution reaction catalysts. Silicides then can be another promising electrocatalysts family as carbides, wherein carbon has the same electronic configuration as silicon. All explored silicides electrodes exhibited low overpotentials (34-54 mV at 10 mA cm-2 ) with Tafel slopes from 23.6 to 32.3 mV dec-1 , which are comparable to that of the commercial 20 wt% Pt/C (37 mV, 26.1 mV dec-1 ). First-principles calculations demonstrated that the superior performance can be attributed to the high catalytic reactivity per site that can even function at high hydrogen coverages (≈100%) on multiple low surface energy facets. The work sheds light on a new class of electrocatalysts for hydrogen evolution, with earth-abundant and inexpensive silicon-based compounds.

High-entropy alloys for water oxidation: a new class of electrocatalysts to look out for.

High-entropy alloys (HEAs) with five or more elements can provide near-continuous adsorption energies and can be optimized for superior persistent catalytic activity. This report presents electrochemical water oxidation facilitated by employing graphene and FeCoNiCuCr HEA nanoparticle based composites prepared via the mechanical milling of graphite-metal powders. The composite efficiently facilitates water oxidation with a low overpotential of 330 mV at 10 mA cm-2, and high specific and mass activities (∼143 mA cm-2 and 380 mA mg-1, respectively, at 1.75 V). Importantly, the composites exhibit excellent accelerated cycling stability with ∼99% current retention (after 3250 cycles). The HEA-based composites are anticipated to replace noble/precious metal based traditional electrocatalysts in the future, the use of which is a major obstacle in the technological scalability of electrochemical energy conversion and storage devices.

Synthesis of highly electroactive nanoflowers like manganesetin oxide and electroanalytical application for chloramphenicol determination in milk and honey samples

Abstract In this report, we have described the disposable electrochemical sensor for the detection of chloramphenicol (CMP) based on MnSnO3 NFs (MSO NFs) modified glassy carbon electrode (GCE). MSO NFs were successfully synthesized through a simple and low-cost coprecipitation approach. FE-SEM, HR-TEM, FTIR, and XRD are used to examine the physical and chemical properties of as-synthesized MSO NFs. The electrochemical activity and performance of the proposed electrode towards the CMP sensor is explored by electrochemical techniques namely CV and DPV. The MSO NFs fabricated electrode showed a rapid current response towards CMP reduction. Under the optimum condition, a linear range is 0.003 μM to 92.21 μM, with low detection limit is calculated is 1 nM. In addition, the proposed sensor has achieved good reproducibility, and excellent selectivity, long-term stability. It was applied to the determination of CMP in spiked milk and honey food samples with satisfactory results. This result demonstrated the MSO NFs was potentially possible for practical applications. All these features, suggest that the MSO NFs is a promising candidate as a new class of electrocatalyst for the highly selective electrochemical sensor for CMP.

Binary metallic sponges as an efficient electrocatalyst for alkaline water electrolysis

Binary metallic sponges comprising of nickel–cobalt (NiCo) hydroxide/oxide composites are prepared using a simple pyrolysis method by employing cyanocobalamin as a new sacrificial template. Subsequently these highly porous materials are demonstrated as an efficient electrocatalyst for oxygen evolution reaction (OER) under alkaline conditions. Structure, morphology and porosity of these materials are controlled through thermal oxidation between 200 and 600 °C and the resultant materials are designated as NiCo-200, NiCo-400 and NiCo-600 respectively. Among the different materials studied in this work, NiCo-200 exhibits better electrocatalytic behaviour for OER with a lower overpotential of 420 mV for obtaining a current density of 10 mA/cm2 along with a turnover frequency value of 0.0234 s−1. The observed higher electrocatalytic activity is attributed to the presence of hydrophilic surface, enriched pores and crystalline nature of NiCo-200. Further the stability studies carried out under alkaline medium at a fixed current density of 20 mA/cm2 showed that both NiCo-200 and NiCo-600 displayed a good stability and retain OER characteristics for a longer duration. Finally our results clearly show that the binary metallic hydroxide/oxide sponges could potentially act as a new class of electrocatalyst in energy conversion devices mainly for alkaline water electrolysis. Highly porous, binary Ni–Co metallic hydroxide/oxide sponges are prepared through a novel route using cyanocobalamin as a sacrificial bio-source. Structure, morphology and porosity of these metallic sponges are controlled by temperature. Further these cost-effective materials are explored as electrocatalysts for oxygen evolution reaction associated with alkaline water electrolysis.

Glycerol Oxidation Catalyzed by High-valency Ruthenium Species at Electrochemical Interfaces

Herein we report high-valency ruthenium (Ru) species as a new class of electrocatalyst for glycerol oxidation. In this study, Ru-modified covalent triazine framework (Ru-CTF) and ruthenium oxide su...

(Invited) Precious Metal-Free Electrocatalysis: Accomplishments and Challenges

In this short presentation, we will concentrate on entirely precious metal-free electrocatalysts as potential alternatives to the incumbent platinum group metal (PGM) materials for electrochemical reactions occurring in acidic, relevant to the energy conversion and storage: (i) oxygen reduction reaction (ORR), (ii) hydrogen evolution reaction (HER) and, time permitted, (iii) hydrogen peroxide generation (“two-electron ORR”). In the first part of this presentation, we will offer a summary of the development of non-precious metal ORR catalysts, emphasizing in particular the approaches that aim at improving the ORR active-site density and understanding of the origins of electrocatalytic activity of non-precious metal catalysts in oxygen reduction as a prerequisite for further development of this class of catalysts. We will focus on metal-nitrogen-carbon (M-N-C) catalysts obtained via the high-temperature treatment of organic precursors of carbon and nitrogen and inorganic precursors of a transition metal, which have been under development at Los Alamos for over a decade and have consistently exhibited the highest ORR activity in both electrochemical-cell and fuel cell testing to date. The second part of this presentation will be devoted to less frequently studied electrocatalysts based on small organic molecules as materials for hydrogen evolution reaction and hydrogen peroxide generation in a two-electron ORR. Unlike the oxygen reduction reaction catalysts in the first part of the talk, these HER/two-electron ORR catalysts are entirely metal-free and have been obtained by a low-temperature synthesis route. In addition to exhibiting a promising activity in electrochemical testing these catalysts show good performance durability over several days of continuous operation. The density functional theory (DFT) calculations have been performed to gain an insight into the reaction mechanisms of HER and two-electron ORR on various conformations of one selected organic molecule. The calculations have revealed thermodynamically favorable reaction pathways and structure-activity relationships, which can guide future synthesis of this new class of electrocatalysts. Acknowledgements Financial support of this research by the U.S. Department of Energy via Fuel Cell Technologies Office (FCTO) and by Los Alamos National Laboratory via Laboratory Directed Research and Development (LDRD) program is gratefully acknowledged.

Water-soluble and air-stable [2Fe-2S]-metallopolymers: A new class of electrocatalysts for H2 production via water splitting

[2Fe–2S] organometallic complexes are effective electrocatalysts for the reduction of weak acids in acetonitrile to generate molecular hydrogen (H2) (hydrogen evolution reaction, HER). Incorporation of such a [2Fe–2S] catalytic site into metallopolymers has been achieved using atom transfer radical polymerization (ATRP). These well-defined polymers have been structurally characterized by SEC, 1H NMR and IR spectroscopy. These metallopolymers catalyze the electrochemical reduction of acetic acid in acetonitrile. In addition, [2Fe–2S] metallopolymers appended with amino groups were shown to be water-soluble and potent electrocatalysts for H2 production at pH 7. In addition to the exceptional activity of these [2Fe–2S] metallopolymers in water, these catalysts maintain catalytic activity in air unlike comparable molecular catalysts.

New Class of Electrocatalysts Based on 2D Transition Metal Dichalcogenides in Ionic Liquid.

The optimization of traditional electrocatalysts has reached a point where progress is impeded by fundamental physical factors including inherent scaling relations among thermokinetic characteristics of different elementary reaction steps, non-Nernstian behavior, and electronic structure of the catalyst. This indicates that the currently utilized classes of electrocatalysts may not be adequate for future needs. This study reports on synthesis and characterization of a new class of materials based on 2D transition metal dichalcogenides including sulfides, selenides, and tellurides of group V and VI transition metals that exhibit excellent catalytic performance for both oxygen reduction and evolution reactions in an aprotic medium with Li salts. The reaction rates are much higher for these materials than previously reported catalysts for these reactions. The reasons for the high activity are found to be the metal edges with adiabatic electron transfer capability and a cocatalyst effect involving an ionic-liquid electrolyte. These new materials are expected to have high activity for other core electrocatalytic reactions and open the way for advances in energy storage and catalysis.

Energy Production and Storage Promoted by Organometallic Complexes

Organometallic complexes have intrinsically excellent characteristics as a new class of electrocatalyst for clean energy production in fuel cells and electrolyzers. The state‐of‐the‐art materials for these devices are based on precious metal nanoparticles dispersed on conductive carbon‐based supports. Although such materials have reached very high performance levels in terms of activity and stability, they suffer from some intrinsic limitations that contribute to hinder the commercial development of fuel cells and electrolyzers on a large scale. Organometallic‐based electrocatalysts may help to overcome such limitations. For example, they exhibit high selectivity in alcohol and sugar electrooxidation. Additionally, precious metal loadings can be reduced significantly using single site organometallic catalysts where each metal atom is potentially active. In this review, we will discuss various literature examples of organometallic electrocatalysts employed as anodes for fuel cells and electrolyzers and as cathodes for the hydrogen evolution reaction (HER). We will focus our attention on the few examples of electrocatalysts that have been successfully used in complete cells.

Synthesis and Characterization of Zirconium Dioxide Anchored Carbon Nanofiber Composite for Enhanced Electrochemical Determination of Chloramphenicol in Food Samples

We developed the zirconium dioxide anchored carbon nanofiber (ZrO2/CNF) composite modified glassy carbon electrode (GCE) for the enhanced and selective electrochemical determination of chloramphenicol (CPL). The as-prepared composite was characterized by different analytical and spectroscopic techniques. The voltammetry techniques were used to evaluate the electrochemical activity of ZrO2/CNF composite. Its electrochemical behavior and the roles of ZrO2 and CNF in the composite toward electrochemical reduction of CPL were elucidated and demonstrated using voltammetry techniques. The ZrO2/CNF modified GCE displayed the enhanced electrocatalytic behavior and reduction peak current response toward for the detection of CPL than that of other modified electrodes. The detailed electrochemical reasons on such excellent performance were also discussed. Differential pulse voltammetry (DPV) is a suitable electrochemical technique to measure CPL reduction, which determined the CPL in the linear range from 0.005 to 903.76 μM and with the lowest detection limit (LOD) of 0.0018 μM. The ZrO2/CNF modified GCE shows its excellent selectivity toward CPL in the presence of antibiotics and sulfa drug. Also, the viability of the raised method has been preliminarily examined by the analysis of CPL in real spiked samples. All these features indicate that the ZrO2/CNF composite is a promising candidate as a new class of electrocatalyst in the development of highly selective CPL electrochemical sensor.

A general strategy to the synthesis of carbon-supported PdM (M = Co, Fe and Ni) nanodendrites as high-performance electrocatalysts for formic acid oxidation

Rational synthesis of a new class of electrocatalysts with high-performance and low-cost is of great significance for future fuel cell devices. Herein, we demonstrate a general one-step simultaneous reduction method to prepare carbon-supported PdM (M = Co, Fe, Ni) alloyed nanodendrites with the assistance of oleylamine and octadecylene. The morphology, structure and composition of the obtained PdM nanodendrites/C catalysts have been fully characterized. The combination of the dendritic structural feature and alloyed synergy offer higher atomic utilization efficiency, excellent catalytic activity and enhanced stability for the formic acid oxidation reaction (FAOR). Strikingly, the as-synthesized PdCo nanodendrites/C catalyst could afford a mass current density of 2467.7 A g−1, which is almost 3.53 and 10.4 times higher than those of lab-made Pd/C sample (698.3 A g−1) and commercial Pd/C catalyst (237.6 A g−1), respectively. Furthermore, the PdCo nanodendrites/C catalyst also exhibit superior stability relative to the Pd/C catalysts, make it a promising anodic electrocatalyst in practical fuel cells in the future. Additionally, the present feasible synthetic approach is anticipated to provide a versatile strategy toward the preparation of other metal alloy nanodendrites/carbon nanohybrids.