Advanced Electrocatalysts Research Articles

Interfacial coupling and dopant-induced electronic modulation enabling Mn–CoP/MXene heterostructures to reduce alkaline HER energy barriers

Electronic structure modulation is a promising strategy to reduce energy barriers of hydrogen evolution reaction (HER). We have constructed 3D monodispersed Mn doped CoP nanoflowers supported on MXene sheets (Mn–CoP/MXene) to boost the alkaline HER kinetics, and the enhanced mechanisms were clarified by photoelectron spectroscopies tests and density functional calculations. The Mn doping and MXene coupling resulted in the modulated electronic structure and, thus, improved active sites for balancing the free energy of H2O dissociation and *H intermediates. The HER activity has been strengthened by the synergy of Mn doping and MXene coupling with an overpotential of only 95 mV to 10 mA cm−2, a ultra-small Tafel slope of 54.1 mV dec−1, and outstanding stability in 1.0 M KOH electrolyte. This work highlights the potential of the synthetic strategy of heteroatom doping and 2D materials coupling to be extended to prepare advanced and cost-effective TMPs-based electrocatalysts.

Hollow nanotube arrays of CoP@CoMoO4 as advanced electrocatalyst for overall water splitting

Developing cost-effective and high-performance bifunctional electrocatalysts for water-splitting in alkaline electrolytes is considered to be one of the prerequisites for exploring hydrogen energy technology. Herein, we present a kind of ZnO template etching strategy coupled with electrodeposition process to prepare MOF-derived CoP@CoMoO4 hollow nanotubes (CoP@CoMoO4 HNTs). The CoP@CoMoO4 HNTs exhibit outstanding electrocatalytic performances, which only require a low potential of 34 and 120 mV to deliver 10 mA cm−2 current density for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Furthermore, the assembled electrolysis system, integrated with the as-prepared CoP@CoMoO4 HNTs, just needs a quite low voltage of 1.51 V to drive 10 mA cm−2 current density and also exhibits excellent durability in alkaline electrolyte for over 24 h. These fascinating electrochemical properties are the results of the unique 3D hollow nanostructure, various heterogeneous interfaces between CoP and CoMoO4 as well as strong electronic configurations of the CoP@CoMoO4 HNTs catalyst. This work emphasizes the key roles of synergism in promoting electrocatalytic reaction kinetics and provides a new pathway for preparing non-noble-based electrocatalysts with astonishing properties.

Surface engineering of Pt aerogels by metal phthalocyanine to enhance the electrocatalytic property for oxygen reduction reaction

Noble metal aerogels (NMAs) have been widely investigated as electrocatalysts for sustainable energy conversion, while enhancing the catalytic activity and stability of NMAs is conducive to reduce cost and expand their application. Herein, modifying Pt aerogel by metal phthalocyanine (MPc) molecules (Pt aer-MPc) was proposed to improve the oxygen reduction reaction (ORR) performance. Typically, the Pt aer-FePc showed significant improvement in half-wave potential, mass, and specific activity compared to commercial Pt/C. Theoretical calculations revealed that the synergy between FePc molecules and Pt aerogel constructs a new interface to facilitate the reduction of oxygen and weaken the bind energies of oxygen intermediates, thus leading to improved ORR performance. Similar promotion in ORR catalytic property was also observed for Pt nanoparticles and commercial Pt/C with the modification of FePc. Therefore, this work not only provides a universal engineering method of MPc decoration to enhance ORR performance of Pt-based electrocatalysts, but also opens a new pathway for designing advanced ORR electrocatalysts with functional molecules toward critical energy-related applications.

A unique sandwich-structured Ru-TiO/TiO2@NC as an efficient bi-functional catalyst for hydrogen oxidation and hydrogen evolution reactions

Developing active and stable non-Pt electrocatalysts for hydrogen oxidation (HOR) and evolution reactions (HER) are critical for anion exchange membrane fuel cells and water electrolyzers. Herein, we report a highly active and robust electrocatalyst Ru-TiO/TiO2@NC, in which Ru nanoclusters are sandwiched between TiO/TiO2 nanosheets and nitrogen-doped carbon layers. Taking advantage of both the optimized Ru-TiO/TiO2 interaction and the conductive carbon coating layers, the Ru-TiO/TiO2@NC exhibits both exceptional HOR/HER activity and superior stability, outperforming Pt/C in the alkaline solution. The HOR mass activity reaches up to 107.2 A gRu-1 at an overpotential of 50 mV, and the specific exchange current density is 0.271 mA cm−2. The HER overpotential at 10 mA cm−2 is only 39 mV, 34 mV lower than required by Pt/C. More importantly, the Ru-based catalyst exhibits excellent anti-oxidation ability by virtue of the unique sandwich structure. Density functional theory calculations discover that the d-band center of Ru in Ru-TiO/TiO2 is downshifted by 0.29 eV compared to Ru-TiO2, decoupling and optimizing the Had/OHad adsorption on Ru, i.e., Had is promoted, while OHad is inhibited and transferred to TiO/TiO2. As a result, (i) the energy required by the potential determining step of HOR/HER is lowered, and (ii) the anti-oxidation ability of the Ru-TiO/TiO2 is enhanced. This work not only addresses the issue of Ru passivation at high anode potentials but also provides an innovative and versatile approach to designing advanced electrocatalysts.

Facilitating two-electron oxygen reduction with pyrrolic nitrogen sites for electrochemical hydrogen peroxide production

Electrocatalytic hydrogen peroxide (H2O2) production via the two-electron oxygen reduction reaction is a promising alternative to the energy-intensive and high-pollution anthraquinone oxidation process. However, developing advanced electrocatalysts with high H2O2 yield, selectivity, and durability is still challenging, because of the limited quantity and easy passivation of active sites on typical metal-containing catalysts, especially for the state-of-the-art single-atom ones. To address this, we report a graphene/mesoporous carbon composite for high-rate and high-efficiency 2e− oxygen reduction catalysis. The coordination of pyrrolic-N sites -modulates the adsorption configuration of the *OOH species to provide a kinetically favorable pathway for H2O2 production. Consequently, the H2O2 yield approaches 30 mol g−1 h−1 with a Faradaic efficiency of 80% and excellent durability, yielding a high H2O2 concentration of 7.2 g L−1. This strategy of manipulating the adsorption configuration of reactants with multiple non-metal active sites provides a strategy to design efficient and durable metal-free electrocatalyst for 2e− oxygen reduction.

Trace Tungsten Microalloying PtCuCo Medium Entropy Alloys: Substructure Reconstruction-Triggered High-Performance for PEMFC.

Refractory metals (W, Nb, or Mo) microalloying Pt-based alloys with unprecedented performance may serve as advanced electrocatalysts for proton exchange membrane fuel cells (PEMFCs). These alloys are endowed with unique stabilizing substructures or lattice defects through the microalloying effect. Herein, trace W microalloying PtCuCo medium entropy alloys (W-PtCuCo) are reported via a stepwise synthesis strategy, starting with home-made Cu nanowires as sacrificial templates by anhydrous solid-phase milling route, and then followed by galvanic replacement-assisted solvothermal in ethylene glycol (EG). In PEMFC tests, the obtained W-PtCuCo exhibits an ultrahigh peak power density and mass power density (relative to cathode) reaching 2.09Wcm-2 and 20.9WmgPt -1 , respectively. During the accelerated degradation test (ADT), the mass activity just lost only 3% after 30k cycles, much better than the above benchmark catalyst. The microalloying-dependent performances shall be attributed to the presence of abundant stepped surfaces, twisted edges, and other lattice defects terminated by W via substructure reconstruction that indeed alters the electronic structure and strain level of the alloys. This work first provides an atomic-level insight into the microalloying-dependent electrocatalytic performance of Pt-based alloys, which is of great significance for developing next-generation efficient catalysts for PEMFC.

Amorphous antimony oxide as reaction pathway modulator toward electrocatalytic glycerol oxidation for selective dihydroxyacetone production

Achievement of an efficient and stable electrocatalytic glycerol oxidation reaction (EGOR) is limited by a lack of strategies for designing advanced electrocatalysts that satisfy the desired product selectivity, high electrocatalytic activity, and stability. Here, we report that the reaction pathway of EGOR can be modulated by the incorporation of amorphous antimony oxide (SbOx) on the surface of a Pt nanoparticle electrocatalyst (SbOx-Pt), which creates highly selective glycerol oxidation to dihydroxyacetone (DHA), one of the most valuable products of EGOR. The selective control of adsorption behaviors of glycerol oxidation products allows for SbOx to act as a reaction pathway modulator. Moreover, SbOx deposition on a Pt surface also enhances the stability, electrocatalytic activity, and glycerol conversion of the Pt electrocatalyst, and thus promotes the EGOR. As a result, the SbOx-Pt electrocatalyst achieves a high DHA selectivity of 81.1%, which is about 11 times higher than that of commercial Pt/C electrocatalysts.

Flower-like iron sulfide/cobaltous sulfide heterostructure as advanced electrocatalyst for oxygen evolution reaction

Developing efficient non-noble metal catalysts is crucial for promoting the electrochemical production of oxygen from water. In this work, a flower-like FeS/Co3S4 heterostructure composite on carbon cloth can be fabricated with a simple sulfurization method. As-prepared FeS/Co3S4 composite shows excellent oxygen evolution reaction (OER) performance with a low overpotential of 252 mV at 10 mA cm−2 and a small Tafel slope of 58 mV dec−1, better than the FeS and Co3S4 electrodes. In addition, the FeS/Co3S4 composite displays outstanding structural stability with any decay over long-time testing. The improved OER catalytic performance of FeS/Co3S4 composite is ascribed to the increased specific surface area and formation of FeS/Co3S4 heterojunction. Besides, theoretical calculation results also show that the FeS/Co3S4 heterojunction possesses a stronger adsorption ability to ∗OH, which is more favorable to the OER than the single FeS and Co3S4 counterpart. Our work has paved a new way of exploring high-efficient catalysts for OER.

Synthesis of three-dimensional (3D) hierarchically porous iron–nickel nanoparticles encapsulated in boron and nitrogen-codoped porous carbon nanosheets for accelerated water splitting

Designing two-dimensional (2D) porous carbon nanosheets is a promising strategy for enhancing the water-splitting activities of non-noble metal catalysts. In this study, we developed a novel method for synthesizing the novel three-dimensional (3D) hierarchically porous iron–nickel (FeNi) nanoparticles encapsulated in boron (B) and nitrogen (N)-codoped porous carbon nanosheets (denoted as FeNi@BNPCNS). Owing to the advantages of morphology and structure of B and N, 10.31 atom % of B/N active centers were successfully doped into the optimal FeNi@BNPCNS-800 nanosheets. FeNi@BNPCNS-800 exhibited better hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalytic activities than control catalysts in an alkaline solution. However, the HER and OER electrocatalytic activities of FeNi@BNPCNS-800 were slightly lower than 20 wt% Pt/C and RuO2. The FeNi@BNPCNS-800||FeNi@BNPCNS-800 electrolyzer achieved 10 mA cm−2 at 1.514 V, which was 73 mV lower than that of 20 wt% Pt/C||RuO2 electrolyzer (1.587 V). The perfect 3D honeycomb-like architectures, abundant mesopores/defects, and abundant electrocatalytic active sites were attributed to the outstanding water-splitting performances of FeNi@BNPCNS-800 nanosheets. This study provides an efficient strategy for the large-scale, rapid, and low-cost fabrication of 2D porous carbon nanosheets without using any template, surfactant, or expensive raw material, thus presenting a simple approach to design advanced non-noble metal electrocatalysts for water splitting.

Recent Advances in Co-Based Electrocatalysts for Hydrogen Evolution Reaction.

Water splitting is a promising technique in the sustainable "green hydrogen" generation to meet energy demands of modern society. Its industrial application is heavily dependent on the development of novel catalysts with high performance and low cost for hydrogen evolution reaction (HER). As a typical non-precious metal, cobalt-based catalysts have gained tremendous attention in recent years and shown a great prospect of commercialization. However, the complexity of the composition and structure of newly-developed Co-based catalysts make it urgent to comprehensively retrospect and summarize their advance and design strategies. Hence, in this review, the reaction mechanism of HER is first introduced and the possible role of the Co component during electrocatalysis is discussed. Then, various design strategies that could effectively enhance the intrinsic activity are summarized, including surface vacancy engineering, heteroatom doping, phase engineering, facet regulation, heterostructure construction, and the support effect. The recent progress of the advanced Co-based HER electrocatalysts is discussed, emphasizing that the application of the above design strategies can significantly improve performance by regulating the electronic structure and optimizing the binding energy to the crucial intermediates. At last, the prospects and challenges of Co-based catalysts are shown according to the viewpoint from fundamental explorations to industrial applications.

Monolayer High-Entropy Layered Hydroxide Frame for Efficient Oxygen Evolution Reaction.

High-entropy materials with tailored geometric and elemental composition provide a guideline for designing advanced electrocatalysts. Layered double hydroxides (LDHs) is a most efficient oxygen evolution reaction (OER) catalyst. However, due to the huge difference in ionic solubility product, an extremely strong alkali environment is necessary to prepare high-entropy layered hydroxides (HELHs), which results in the uncontrollable structure, poor stability and scarce active sites. Here, wepresent a universal synthesis of monolayer HELH frame in a mild environment, regardless of the solubility product limit. Mild reaction conditions allow usto precisely control the fine structure and elemental composition of the final product. Consequently, the surface area of the HELHs is up to 380.5 m2 g-1 . The current density of 100mA cm-2 is achieved in 1M KOH at an overpotential of 259mV. And after 1000 hours operation at the current density of 20mA cm-2 , the catalytic performance shows no obvious deterioration. The high-entropy engineering and fine nanostructure control open opportunities to solve the problems of low intrinsic activity, very few active sites, instability, low conductance during OER for LDH catalysts. This article is protected by copyright. All rights reserved.

Metal–Organic Framework‐Derived N‐Doped Carbon with Controllable Mesopore Sizes for Low‐Pt Fuel Cells

AbstractMesoporous structure of carbon materials plays an important role in electrocatalyst design. Constructing carbon supports with tunable mesopores has long been a challenge. Herein, the elaborate regulation of mesopores in N‐doped carbon materials is reported by pyrolyzing energetic metal‐triazolate (MET) frameworks with different particle sizes and at different ramp rates. Higher thermal transfer rates brought about by smaller particle size and higher ramp rate lead to more violent decomposition with a large number of gases producing, which in turn result in larger mesopores in the derivatives. Consequently, a series of N‐doped carbon materials with controllable mesopores are obtained. As a proof‐of‐concept, ultrafine Pt nanoparticles are enveloped inside these mesopores to acquire high‐performance electrocatalysts for oxygen reduction reaction. The optimized catalyst achieves high mass activity of 1.52 A mgPt−1 at 0.9 ViR‐free and peak power density of 0.8 W cm−2 (H2‐Air) with an ultralow Pt loading of 0.05 mgPt cm−2 at cathode in fuel cells, highlighting the great advantages of MET‐derived carbon materials with controllable mesopores in the preparation of advanced electrocatalysts.

High-efficiency degradation of carbamazepine by the synergistic electro-activation and bimetals (FeCo@NC) catalytic-activation of peroxymonosulfate

This study developed a novel advanced oxidation process, coupling activation of peroxymonosulfate (PMS) by electrochemistry and catalyst based on an advanced electrocatalyst. Herein, nitrogen-rich porous carbon decorated with FeCo alloy (FeCo@NC) was fabricated to modify carbon felt (FeCo@NC/CF) to remove carbamazepine (CBZ) via electro-enhanced activation of PMS (E-FeCo@NC/CF-PMS). C–C, O-CO and M=O contents in FeCo@NC are positively correlated with CBZ degradation (r2 =0.937 and 0.942). Benefit from the obvious synergistic effect (S=3.49) of electro-activation and catalytic-activation caused by electrowetting, CBZ removal (k = 0.0811 min−1) was significantly improved with extremely low electric energy consumption (EEC, 0.0506 kWh log−1 m−3). Electric field facilitates the regeneration of key catalytic components Fe2+ and Co2+. •OH (derived from the co-activation) and electron-transfer process (derived from catalytic-activation) were the underlying catalysis mechanisms. This work provided new vision to promote the practical utilization of Fenton-like reaction with high-efficiency and low-cost.

Rapid synthesis of nickel–iron-oxide (NiFeOx) solid-solution nano-rods thin films on nickel foam as advanced electrocatalyst for sustained water oxidation

The development of earth-rich, noble-metal-free, and highly electroactive catalysts to accelerate the oxygen evolution reaction (OER) is a formidable challenge for the establishment of water-splitting technologies. Here, a solid-solution nickel-iron oxide (NiFeOx) electrocatalyst is readily grown on a Ni-foam (NF) substrate by a rapid and economical aerosol-assisted chemical vapor deposition process. In particular, the NiFeOx thin film fabricated in 40 min acquires a distinctive nanorod structure and proves to be stable and efficient for OER in alkaline solutions. It is shown that the catalyst needs a low over-potential of 226 mV to reach the typical current density of 10 mA/cm2, and it can approach a remarkable current density level of 1000 mA/cm2 by taking a slightly higher over-potential of 139 mV. The small Tafel slope of 64 mv.dec−1 and splendid electrochemical stability of 40 h at high current densities outperform many known FeNi-based anodes as well as commercial IrO2 and RuO2. The unique structure of the thin film offers many electroactive sites and a high surface area in combination with an improved electrical conductivity of NF, which is believed to play an imperative role in the excellent activity of the catalyst. The cost-effective and simple strategy to fabricate NiFeOx nano-fibrous is very attractive for the development of electrocatalysts for water splitting.

Designing and regulating catalysts for enhanced oxygen evolution in acid electrolytes

AbstractThe proton exchange membrane (PEM) water electrolyzer has been considered a versatile approach for practical H2 production. However, the oxygen evolution reaction (OER) in acid media with complicated proton‐coupled electron transfer steps possesses sluggish kinetics and high reaction barriers, severely hindering the development of PEM water electrolyzers. Consequently, high‐efficient Ru‐ and Ir‐based catalysts have always been essential to accelerate the OER rate and lower the reaction barrier in PEM water electrolyzer. Therefore, it is very necessary to construct low‐cost catalysts with excellent electrocatalytic performances to replace these noble metal‐based OER electrocatalysts. In this review paper, a detailed discussion towards fundamentally comprehending the reaction mechanisms of OER was conducted. Accordingly, we proposed the principles of designing advanced OER electrocatalysts with enhanced performances and lowered costs. After that, recent developments in designing various acidic OER electrocatalysts were summarized. Meanwhile, the available regulation strategies about noble metals, nonprecious metals, and metal‐free nanomaterials were presented, which are promising for tuning the electronic structures, boosting the electrocatalytic performances, and reducing the costs of electrocatalysts. We also provided the existing challenges and perspectives of various OER electrocatalysts, hoping to promote the development of PEM water electrolyzers.

Severe Plastic Deformation for Advanced Electrocatalysts for Electrocatalytic Hydrogen Production

Developing electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of water splitting is very important for electrocatalytic hydrogen production. Very recently, emerging study have demonstrated that materials show some superior HER and OER performances of water splitting after processed by severe plastic deformation (SPD). In this work, recent advances on electrochemical hydrogen production performances of materials by SPD are summarized. Some basic principles of electrocatalytic water splitting are briefly described, and then the development of SPD technology and recent advances on SPDed materials with enhanced hydrogen production properties are comprehensively reviewed. Moreover, future direction on SPDed materials for hydrogen production is also prospected.

Vertically molybdenum disulfide nanosheets on carbon cloth using CVD by controlling growth atmosphere for electrocatalysis

Molybdenum disulfide (MoS2) has been deemed as one of the promising noble-metal-free electrocatalysts for hydrogen evolution reaction (HER), but it suffers from the inert basal plane and low electronic conductivity. Regulating the morphology of MoS2 during the synthesis on conductive substrates is a synergistic strategy for enhancing the HER performance. In this work, vertical MoS2 nanosheets were fabricated on carbon cloth (CC) using an atmospheric pressure chemical vapor deposition method. The growth process could be effectively tuned through introducing hydrogen gas during vapor deposition process, resulting in nanosheets with increased edge density. The mechanism for edge-enriching through controlling the growth atmosphere is systematically studied. The as-prepared MoS2 exhibits excellent HER activity due to the combination of optimized microstructures and coupling with CC. Our findings provide new insights to design advanced MoS2-based electrocatalysts for HER.

Hierarchically heterostructured Pt/CrN–TiN derived from metal organic frameworks as an efficient electrocatalyst for methanol oxidation reaction

Exploiting cost-effective and highly efficient electrocatalysts toward methanol oxidation reaction (MOR) is meaningful but challenging. Metal-organic framework (MOF)-based derivatives have attracted much attention of the community in various research fields. Herein, a novel metal-organic framework derived three dimensional (3D) heterostructure (Pt/CrN–TiN) has been synthesized as an efficient MOR electrocatalyst through interfacial engineering. Benefiting from the unique 3D penetrating structure and the abundant heterogeneous interfaces, the Pt/CrN–TiN heterostructure exposed maximum active sites, open diffusion channels, and accelerated electron transfer at heterogeneous interfaces, thus modulating adsorption/desorption behavior of targeted reactants/intermediates and eventually facilitating the MOR kinetics. Impressively, the designed Pt/CrN–TiN catalyst performed high catalytic activity toward methanol oxidation reaction (1.14 A mgpt−1) compared to that of Pt/CrN (0.18 A mgpt−1), Pt/TiN (0.64 A mgpt−1) and Pt/C (0.44 A mgpt−1), respectively. Density functional theory (DFT) calculations reveal that the existing heterointerfaces optimize the free energy of intermediates during MOR, accelerating the reaction kinetics. We believe that the current work provides new insight and useful guidance for fabricating advanced electrocatalysts.

Recent Advances in Electrocatalysts for Efficient Nitrate Reduction to Ammonia

AbstractAmmonia as an irreplaceable chemical has been widely demanded to keep the sustainable development of the modern society. However, its industrial production consumes huge energy and releases extraordinary green‐house gases, leading to various environmental issues. To achieve the green production of ammonia is a great challenge that has been extensively pursued recently. In the review, a most promising strategy, electrochemical nitrate reduction reaction (e‐NO3RR) for the purpose is comprehensively investigated to give a full understanding of its development and mechanism and provide guidance for future directions. Particularly, the development of electrocatalysts is focused to realize the high ammonia yield rate and Faraday efficiency for industrial applications. The recent‐developed catalysts, including noble metallic materials, alloys, metal compounds, single‐metal‐atom catalysts, and metal‐free materials, are systematically discussed to review the effects of various factors on the catalytic performance in e‐NO3RR. Accordingly, the strategies, including defects engineering, coordination environment modulating, surface controlling, and hybridization, are carefully discussed to improve the catalytic performance, such as the intrinsic activity and selectivity. Finally, perspectives and challenges are given out. This review shall provide insightful guidance on the development of advanced catalytic systems for the production of green ammonia efficiently in the industry.

Modulating Water Splitting Kinetics via Charge Transfer and Interfacial Hydrogen Spillover Effect for Robust Hydrogen Evolution Catalysis in Alkaline Media.

Designing and synthesizing advanced electrocatalysts with superior intrinsic activity toward hydrogen evolution reaction (HER) in alkaline media is critical for the hydrogen economy. Herein, a novel Ir@Rhene heterojunction electrocatalyst is synthesized via epitaxially confining ultrasmall and low-coordinate Ir nanoclusters on the ultrathin Rh metallene accompanying the formation of Ir/IrO2 Janus nanoparticles. The as-prepared heterojunctions display outstanding alkaline HER activity, with an overpotential of only 17mV at 10mA cm-2 and an ultralow Tafel slope of 14.7mV dec-1 . Both structural characterizations and theoretical calculations demonstrate that the Ir@Rhene heterointerfaces induce charge density redistribution, resulting in the increment of the electron density around the O atoms in the IrO2 site and thus delivering much lower water dissociation energy. In addition, the dual-site synergetic effects between IrO2 and Ir/Rh interface trigger and improve the interfacial hydrogen spillover, thereby subtly avoiding the steric blocking of the active site and eventually accelerating the alkaline HER kinetics.