Exploration Of Electrocatalysts Research Articles

One-step electrodeposition of bifunctional MnCoPi electrocatalysts with wrinkled globular-flowers-like structure for highly efficient electrocatalytic water splitting

The development and exploration of electrocatalysts with the high reactive and abundant availability is still extremely crucial in electrocatalytic overall water splitting. Herein, a novel globular-flowers-like MnO2/Co3(PO4)2 (denoted as MnCoPi) electrocatalyst on nickel foam was successfully prepared through a simple one-step electrodeposition method. The MnCoPi electrocatalyst simultaneously delivers remarkable electrocatalytic activities for hydrogen evolution reaction (HER) with overpotentials (η10) reaching 102 mV and oxygen evolution reaction (OER) with overpotentials (η10) up to 225 mV in 1 M KOH solution. Furthermore, the assembled electrolyzer cell utilizing MnCoPi as the cathode and anode only requires a low voltage of 1.55 V to achieve a current density of 10 mA cm−2. Moreover, the developed MnCoPi electrocatalyst shows excellent stability during continuous operation for 48 h in OER, HER and overall water splitting process. Compared with the pristine MnO2, the significant electrocatalytic properties of MnCoPi can mainly be attributed to the improved physicochemical properties such as distinctive globular-flowers-like morphology, huge specific surface areas and abundant porosity structure, low electrochemical resistance, especially for the formed heterojunction between MnO2 and Co3(PO4)2, which can provide abundant reactive sites and accelerated electron transfer, etc. Consequently, this work provides a new avenue for the development of efficient and stable bifunctional electrocatalysts for overall water splitting.

Advanced Hollow Cubic FeCo-N-C Cathode Electrocatalyst for Ultrahigh-Power Aluminum-Air Battery.

The exploration of electrocatalysts toward oxygen reduction reaction (ORR) is pivotal in the development of diverse batteries and fuel cells that rely on ORR. Here, a FeCo-N-C electrocatalyst (FeCo-HNC) featuring with atomically dispersed dual metal sites (Fe-Co) and hollow cubic structure is reported, which exhibits high activity for electrocatalysis of ORR in alkaline electrolyte, as evidenced by a half-wave potential of 0.907V, outperforming that of the commercial Pt/C catalyst. The practicality of such FeCo-HNC catalyst is demonstrated by integrating it as the cathode catalyst into an alkaline aluminum-air battery (AAB) paring with an aluminum plate serving as the anode. This AAB demonstrates an unprecedented power density of 804mWcm-2 in ambient air and an impressive 1200mWcm-2 in an oxygen-rich environment. These results not only establish a new benchmark but also set a groundbreaking record for the highest power density among all AABs reported to date. Moreover, they stand shoulder to shoulder with state-of-the-art H2-O2 fuel cells. This AAB exhibits robust stability with continuous operation for an impressive 200 h. This groundbreaking achievement underscores the immense potential and forward strides that the present work brings to the field.

Defect‐Derived Catalysis Mechanism of Electrochemical Reactions in Two‐Dimensional Carbon Materials

In the past decades, remarkable progress has been achieved in the exploration of electrocatalysts with high activity, long durability, and low cost. Among these, defective graphene (DG)‐based catalysts are considered as one of the most potential substitutes for precious metal‐based electrocatalysts. DG‐based catalysts contain abundant active centers with different configurations resulting from their extraordinary high‐structural tunability. Herein, an overview on recent advancements in developing four kinds of DG‐based catalysts is presented: 1) heteroatoms‐doped graphene; 2) intrinsic DG (vacancy and topological defect); 3) nonmetal atoms or/and metal species‐modified intrinsic DG (heterogeneous species and intrinsic defects co‐tuned DG); and 4) DG‐based van der Waals‐type multilayered heterostructures. In particular, the synergistic effects between various defects are discussed, and the origin of catalytic activity is reviewed. Meanwhile, the established defect‐derived catalytic mechanism is summarized, which is beneficial for the rational design and fabrication of high‐performance electrocatalysts for practical energy‐related applications. Finally, challenges and future research directions on defect engineering in noble metal‐free materials for electrocatalysis are proposed.

Fabrication of grass-like FeCoNiP/copper foam electrodes via cyclic voltammetry toward efficient overall water splitting reaction

Exploration of electrocatalysts with excellent activity and durability, facile scale-up and low cost is one of the most crucial issues for water splitting. Ternary FeCoNi phosphides were obtained by electrodeposition of FeCoNi hydroxides on copper foam (CF) via cyclic voltammetry and followed by low-temperature phosphorization. Benefiting from synergistic effects between simultaneous presence of multi-metallic active centers and three-dimensional substrate of copper foam, FeCoNiP/CF exhibits an ultralow overpotential of 48 mV for hydrogen evolution reaction (HER) and 228 mV for oxygen evolution reaction (OER) to deliver a current density of 10 mA cm−2 in 1.0 M KOH solution, and its Tafel slopes are respectively 93.46 and 87.84 mV dec−1 for HER and OER, indicating outstanding electrocatalytic activity as a bifunctional electrocatalyst. An electrolyzer assembled by this catalyst demonstrates cell voltages of 1.52 and 2.08 V at current densities of 10 and 200 mA cm−2, respectively. Remarkably, the durability of FeCoNiP/CF measured by chronoamperometry test can maintain 96.4% after 120 h, indicating excellently long-term stability. The performances of FeCoNiP/CF are much better than those of FeCoNiP powder catalyst obtained by hydrothermal-phosphorization and other bimetallic phosphides, due to its uniquely grass-like morphology and synergetic effects of various metallic active centers. This research can provide an effective strategy of mass production of electrodes with prominent catalytic activity and stability for overall water splitting reaction.

Superstructures of Zeolitic Imidazolate Frameworks to Single- and Multiatom Sites for Electrochemical Energy Conversion.

The exploration of electrocatalysts with high catalytic activity and long-term stability for electrochemical energy conversion is significant yet remains challenging. Zeolitic imidazolate framework (ZIF)-derived superstructures are a source of atomic-site-containing electrocatalysts. These atomic sites anchor the guest encapsulation and self-assembly of aspheric polyhedral particles produced using microreactor fabrication. This review provides an overview of ZIF-derived superstructures by highlighting some of the key structural types, such as open carbon cages, 1D superstructures, hollow structures, and the interconversion of superstructures. The fundamentals and representative structures are outlined to demonstrate the role of superstructures in the construction of materials with atomic sites, such as single- and dual-atom materials. Then, the roles of ZIF-derived single-atom sites for the electroreduction of CO2 and electrochemical synthesis of H2 O2 are discussed, and their electrochemical performance for energy conversion is outlined. Finally, the perspective on advancing single- and dual-atom electrode-based electrochemical processes with enhanced redox activity and a low-impedance charge-transfer pathway for cathodes is provided. The challenges associated with ZIF-derived superstructures for electrochemical energy conversion are discussed.

A special Bi-S motif catalyst for highly selective CO2 conversion to methanol

Carbon dioxide as raw materials chemically transformed to valuable, renewable and high-energetic carbon feedstocks, especially if driven by renewable energy, is a desirable way to mitigate the depletion of fossil fuels and allow environmentally neutral use of carbon fuels. However, it remains more exploration of electrocatalysts with high activity and superior selectivity in converting CO2 to storable carbon-based liquid fuels, like methanol. Herein, we develop an in-situ sulfurizing strategy over the Bi-based metal-organic frameworks (Bi-BTC) and disperse stable and special Bi-S motif on subsequent S-doped carbon-framework (called BS@Cx). Unlike the previous reports on Bi-based catalysts, as-prepared BS@Cx converted CO2 to methanol as major product at the whole applied potentials. Benefiting from the special Bi-S motif, it brought to the dramatic selectivity change of CO2 reduction production: dramatic decrease in HCOO− selectivity and increase in methanol selectivity. At −0.9 V vs RHE, maximum methanol faradaic efficiency (FE) and the selectivity of methanol arrived at 78.6% and 78.8%(Total-C FE was 95.5%), respectively. Some effective experiments involving of ECSA and charge transfer efficiency (Φ) certified that BS@Cx catalysts in the form of Bi-S motif exhibited higher intrinsic activity and selectivity, and overcame the energy barrier for methanol production. Coupled with PDOS of catalyst absorbed intermediates (OCHO* and CO*) and discussion of intermediates (COOH* and CH2O*), we bring forward a new possible pathway for catalyzing CO2 to methanol over BS@800. Further though microkinetic analysis with experimental Tafel slopes, we provided first-order understanding on the proposed reaction mechanisms, such as the rate-determining steps (RDS) and surface coverage (θ) of major reaction intermediates, and shed light on how rate-limiting steps can give rise to different Tafel slopes. This work may occur worthy insights into crystal structure engineering to achieve efficient electrocatalysts for selective CO2 conversion toward generation of valuable carbon-based chemicals.

A BiPb bimetallic electrode for highly selective CO2 conversion to formate

Electrochemical CO2 reduction technology can chemically transfer carbon dioxide into high value-added chemicals and fuels by utilizing renewable energy. However, it still needs more exploration of electrocatalysts with high activity, superior selectivity, and excellent durability in converting CO2 to storable carbon-based liquid fuels. Herein, we develop a BiPb bimetallic electrode with metal Bi and alloy Pb7Bi3 crystalline phase by a pulse-electrodeposition method with multiple cycles. The prepared BiPb electrode can generate a high catalytic selectivity and activity for the electroreduction CO2 to formate with good current density (15.56 mA cm−2) at −0.96 V vs RHE and desired long-term durability. The BiPb has higher formate ECSA-normalized partial current densities than single Bi and Pb at the whole potential range, suggesting that it possesses higher intrinsic activity and selectivity toward formate production. Furthermore, during the long-term test, the crystalline phase of the BiPb electrode would transform from metal Bi and Pb7Bi3 into Bi2O2CO3 because the BiPb is exposed in CO2-rich 0.5 M KHCO3 electrolyte at −0.96 V vs. RHE. This work may arouse worthy interests in mixed crystals of the bimetallic electrode to achieve efficient electrocatalysts for selective CO2 conversion toward the generation of valuable carbon-based chemicals.

Process of metal-organic framework (MOF)/covalent-organic framework (COF) hybrids-based derivatives and their applications on energy transfer and storage.

The fossil-fuel shortage and severe environmental issues have posed ever-increasing demands on clean and renewable energy sources, for which the exploration of electrocatalysts has been a big challenge toward energy transfer and storage. Some indispensable features of electrocatalysts, such as large surface area, controlled structure, high porosity, and effective functionalization, have been proved to be critical for the improvement of electrocatalytic activities. Recently, the rapid expansion of metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and porous-organic polymers has provided extensive opportunities for the development of various electrocatalysts. Moreover, combining diverse descriptions of porous-organic frameworks (such as MOFs and COFs) can generate amazing and fantastic properties, affording the formed MOF/COF (including core-shell MOF@MOF and MOF@COF and layer-on-layer MOF-on-MOF or COF-on-MOF) heterostructures wide applications in diverse fields, especially in clean energy and energy transfer. To further boosts electronic conductivity, catalytic performances, and energy storage abilities, these MOF/COF hybrid materials have been widely utilized as versatile precursors for the manufacture of transition metal catalysts embedded within mesoporous carbon nitrides (M@CNx) and porous carbon nitride frameworks (CNx) via a facile pyrolysis process. Given that these M@CNx and CNx hybrids are composed of abundant catalytic centers, rich functionalities, and large specific surface areas, vast applications in energy transfer and energy storage fields can be realized. In this mini-review, we summarize the preparation strategies of MOF/COF-based hybrids, as well as their derivatives, nanostructure formation mechanism of M@CNx and CNx hybrids from MOF/COF-based hybrid materials, and their applications as catalysts for driving diverse reactions and electrode materials for energy storage. Further, current challenges and future prospects of applying these derivatives into energy conversion and storage devices are also discussed.

Low-cost single-atom transition metals on two-dimensional SnO nanosheets for efficient hydrogen evolution catalysis in all pH-range

The exploration of electrocatalysts with high performance of hydrogen evolution reaction (HER) in all media is essential for developing clean energies. Single-atom catalysts (SACs) have attracted wide attentions owing to their maximum atom utilization and excellent catalytic activity. In this work, the HER activities of transition metal (TM) (TM = Fe, Co, Ni and Cu) SACs on two-dimensional SnO monolayer are studied using density functional theory. We found that the low-cost TM SACs can exhibit high HER activity in wide pH-range. Especially, Co SACs show promising catalytic activity with the Gibbs free energy of hydrogen adsorption (ΔGH∗) as low as ∼ 0.015 eV, which are also high active in either acidic or alkaline environments. With the experimentally inevitable oxygen vacancies in SnO, the ΔGH∗ of Co, Ni and Cu SACs are almost zero, which are competitive with the precious catalyst Pt(111) (-0.09 eV). The exceptional HER activity is correlated to the enhanced electron states close to the Fermi level as well as the d-band center positions of the TM. Our work opens new avenues for engineering low-cost TM SACs with pH-universal HER performance, which is of great importance in practical applications.

Synergistic Coupling of NiTe Nanoarrays with FeOOH Nanosheets for Highly Efficient Oxygen Evolution Reaction

AbstractHydrogen is the most promising alternative energy source in the face of energy crisis, and water splitting is a green strategy for hydrogen generation. The oxygen evolution reaction (OER) is the essential half‐reaction in electrochemical water splitting, and thus development and exploration of electrocatalysts with excellent performance are vital to prompt the application of OER. Due to the unique electronic properties of NiTe and strong synergistic interaction between NiTe and FeOOH, NiTe@FeOOH hybrid nanorods were successfully fabricated on Ni foams (NF) by a hydrothermal reaction step and another in‐situ growth step for the first time without consuming any extra energy. The 3D structure of the NiTe@FeOOH/NF was confirmed by powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS) mapping technologies. Electrochemical measurements showed that the as‐prepared NiTe@FeOOH/NF needs only an overpotential of 241 mV to achieve a current density of 10 mA cm−2 in 1.0 M KOH and requires 1.341 V to drive 10 mA cm−2 in 1 M KOH with a 0.33 M urea, showing excellent long‐term stability. The NiTe@FeOOH/NF as the bifunctional electrocatalyst in an electrolyzer shows high efficiency with a cell voltage of 1.50 V at 10 mA cm−2. This work can provide a new efficient method to construct highly active and cost‐effective OER catalysts.

Monoclinic Scheelite Bismuth Vanadate Derived Bismuthene Nanosheets with Rapid Kinetics for Electrochemically Reducing Carbon Dioxide to Formate

AbstractElectrochemical reduction of CO2 to high‐value chemical feedstocks, such as formate, is one of the most promising ways to alleviate the greenhouse effect. Unfortunately, the exploration of electrocatalysts with high activity and selectivity over a wide potential window (especially low potential for high current density) still remains a grand challenge. In this study, the fabrication of bismuthene nanosheets using an in‐situ electrochemical transformation strategy of monoclinic scheelite BiVO4 flakes is demonstrated. Catalyzing the CO2 electroreduction in 1 m KHCO3 aqueous solution, the bismuthene nanosheets exhibit a dramatically high formate Faradaic efficiency (FE) of ≈97.4% and a very large current density of −105.4 mA cm−2 at −1.0 V versus reversible hydrogen electrode. Significantly, over a record wide potential window of 750 mV from the initial −0.65 V to the applied minimum −1.4 V, the formate FEs of the bismuthene nanosheets are always higher than 90%, outperforming state‐of‐the‐art electrocatalysts. Both experimental and theoretical investigations reveal that, in comparison with •COOH and H• intermediates, the bismuthene nanosheets preferentially promote fast reaction kinetics towards HCOO•, which eventually accelerates the production of formate.

Mixed-metal MOF-derived Co-doped Ni3C/Ni NPs embedded in carbon matrix as an efficient electrocatalyst for oxygen evolution reaction

The exploration of electrocatalysts with high oxygen evolution reaction (OER) activity is highly desirable and remains a significant challenge. Transition metal carbides (TMCs) have been investigated as remarkable hydrogen evolution reaction (HER) electrocatalysts but few used as oxygen evolution reaction (OER) electrocatalysts. Herein, a Co doped Ni3C/Ni uniformly dispersed in a graphitic carbon matrix was prepared by pyrolysis of a metal organic framework (Co/Ni-MOF) under a flow of Ar/H2 at 350 °C, and Ni3C/Ni@C was also prepared for comparison. The various characterization techniques confirmed the successful preparation of the heteroatom doped TMCs-based catalysts by pyrolysis of MOFs. Co doped Ni3C/Ni@C exhibited superior electrocatalytic properties for OER. For example, Co–Ni3C/Ni@C depicts a lower overpotential and smaller Tafel slope than Ni3C/Ni@C and IrO2 during the OER in 1 M KOH solution, additionally, it shows a higher active surface area than Ni3C/Ni@C. The outstanding electrocatalytic performance of Co-doped Ni3C/Ni@C in the OER was mainly ascribed to the synergistic effect of the Co and Ni3C/Ni active sites.

Improving electrocatalytic activity of iridium for hydrogen evolution at high current densities above 1000 mA cm−2

The exploration of electrocatalysts with high activity and durability for hydrogen evolution reaction (HER) at extremely high current densities above 500 mA cm−2 in alkaline media is the basis for large-scale industrial applications. Plain Ir possesses optimum performance for OER in alkaline electrolytes but presents a noticeable underperforming HER activity. Herein, the strategy by pyrolyzing Ir-modified metal-organic frameworks (MOFs) precursors has been employed in designing electrocatalysts consisting of IrFe nanoalloys supported on N-doped carbon layers. The catalyst requires a small overpotential of 105 mV to deliver a current density of 100 mA cm-2 in basic media, which surpasses that of commercial Ir/C and Pt/C benchmarks. Particularly, the catalyst also exhibits an extraordinary performance with low overpotential of only 850 mV at 1000 mA cm-2. The extraordinary performance originates from superior conductivity, the modulated electronic structure and large specific surface area.

MOF Template‐Directed Fabrication of Hierarchically Structured Electrocatalysts for Efficient Oxygen Evolution Reaction

The ever‐increasing demand for clean and renewable power sources has sparked intensive research on water splitting to produce hydrogen, in which the exploration of electrocatalysts is the central issue. Herein, a new strategy, metal–organic framework template‐directed fabrication of hierarchically structured Co3O4@X (X = Co3O4, CoS, C, and CoP) electrocatalysts for efficient oxygen evolution reaction (OER) is developed, where Co3O4@X are derived from cobalt carbonatehydroxide@zeolitic‐imidazolate‐framework‐67 (CCH@ZIF‐67). Unique hierarchical structure and synergistic effect of resulting catalysts endow abundant exposed active sites, facile ion diffusion path, and improved conductivity, being favorable for improving catalytic activity of them. Consequently, these derivatives Co3O4@X reveal highly efficient electrocatalytic performance with long‐term durability for the OER, much superior to previously reported cobalt‐based catalysts as well as the Ir/C catalyst. Particularly, Co3O4@CoP exhibits the highest electrocatalytic capability with the lower overpotential of 238 mV at the current density of 10 mA cm−2. Furthermore, Co3O4@X can also efficiently catalyze other small molecules through electro‐oxidation reaction (e.g., glycerol, methanol, or ethanol). It is expected that the strategy presented here can be extended to the fabrication of other composite electrode materials with hierarchical structures for more efficient water splitting.