Rational Design Of Efficient Electrocatalysts Research Articles

Rational structure design of FeCo-based materials as efficient electrodes for overall water-splitting

Rational design of efficient electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential to promote the performance of overall water-splitting. In this work, we demonstrate the high performance electrolyzer by using Fe–Co phosphide grown on Ni foam (FeCoP/NF) as HER electrode and self-supported FeCo2O4@FeCo2S4/NF heterostructure as OER electrode. Thanks to the more active sites and faster charge transfer capability, the FeCoP/NF electrode can deliver low HER overpotentials of 59.6 and 233.6 mV at 10 and 100 mA cm[Formula: see text]. Furthermore, the synergistic effect at interfaces also endows low overpotentials of FeCo2O4@FeCo2S4/NF at specific current densities. As a result, the designed FeCoP/NF——FeCo2O4@FeCo2S4/NF device just needs a voltage of 1.52 V to afford 10 mA cm[Formula: see text], indicating greatly potential in practical application.

Highly Efficient Oxygen Evolution Reaction Enabled by Phosphorus Doping of the Fe Electronic Structure in Iron-Nickel Selenide Nanosheets.

The electronic structure of active sites is critically important for electrochemical reactions. Here, the authors report a facile approach to independently regulate the electronic structure of Fe in Ni0.75Fe0.25Se2 by P doping. The resulting electrode exhibits superior catalytic performance for the oxygen evolution reaction (OER) showing a low overpotential (238 mV at 100 mA cm−2, 185 mV at 10 mA cm−2) and an impressive durability in an alkaline medium. Additionally, the mass activity of 328.19 A g−1 and turnover frequency (TOF) of 0.18 s−1 at an overpotential of 500 mV are obtained for P─Ni0.75Fe0.25Se2 which is much higher than that of Ni0.75Fe0.25Se2 and RuO2. This work presents a new strategy for the rational design of efficient electrocatalysts for OER.

Designing efficient single-atomic catalysts for bifunctional oxygen electrocatalysis via a general two-step strategy

The rational design of efficient electrocatalysts based on comprehensive mechanistic insights is crucial to widespread penetration of future sustainable and eco-friendly energy technologies. Herein, via systematic first-principles calculations, we propose a general two-step strategy for developing highly active single-atom catalyst (SACs) supported on a prototypical substrate (g-C3N4) for bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Our results show that the intrinsic activity can be properly evaluated by a robust screening rule, and, particularly, the descriptor can be readily calculated by a few handy and basic properties. According to the knowledge, we propose an effective approach (i.e., creating an N vacancy in the cavity of g-C3N4) that enables further activity improvement. Specifically, the predicted ORR/OER activity on Ag and Rh based SACs are comparable or even outperforms that of respective benchmark catalysts. This study not only provides several promising candidates for bifunctional ORR/OER, but also directs a new avenue for rational design of high-performance catalysts.

Recent Progress in Advanced Electrocatalyst Design for Acidic Oxygen Evolution Reaction.

Proton exchange membrane (PEM) water electrolyzers hold great significance for renewable energy storage and conversion. The acidic oxygen evolution reaction (OER) is one of the main roadblocks that hinder the practical application of PEM water electrolyzers. Highly active, cost-effective, and durable electrocatalysts are indispensable for lowering the high kinetic barrier of OER to achieve boosted reaction kinetics. To date, a wide spectrum of advanced electrocatalysts has been designed and synthesized for enhanced acidic OER performance, though Ir and Ru based nanostructures still represent the state-of-the-art catalysts. In this Progress Report, recent research progress in advanced electrocatalysts for improved acidic OER performance is summarized. First, fundamental understanding about acidic OER including reaction mechanisms and atomic understanding to acidic OER for rational design of efficient electrocatalysts are discussed. Thereafter, an overview of the progress in the design and synthesis of advanced acidic OER electrocatalysts is provided in terms of catalyst category, i.e., metallic nanostructures (Ir and Ru based), precious metal oxides, nonprecious metal oxides, and carbon based nanomaterials. Finally, perspectives to the future development of acidic OER are provided from the aspects of reaction mechanism investigation and more efficient electrocatalyst design.

In situ/operando vibrational spectroscopy for the investigation of advanced nanostructured electrocatalysts

• In situ vibrational spectroscopy mainly includes Raman- and FTIR-based techniques. • Vibrational spectroscopy allows for probing catalyst states and reaction dynamics in real-time. • Such techniques can be applied to ORR, OER, HER, NRR, and CO 2 RR processes. Electrochemical energy conversion via electrocatalysis offers promising solutions to tackle problems of global energy crisis and environmental issues. The rational design of efficient electrocatalysts requires an in-depth understanding of the underlying mechanism and the structure-activity relationship of key electrocatalytic processes such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO 2 RR), and nitrogen reduction reaction (NRR). To gain a comprehensive understanding of these electrochemical systems, in situ characterization techniques capable of determining catalyst states as well as important reaction intermediates under operando conditions are necessary. Vibrational spectroscopic methods, including Raman and FTIR-based techniques, are powerful tools to monitor surface transformation, active sites, and interfacial intermediates under reaction conditions. Here, recent developments of in situ / operando vibrational spectroscopic techniques in the probing of various electrochemical reactions and processes are described and summarized. The outlook for future research directions in this field is also discussed. The aim is to attract increasing attention of the wider community to in situ / operando characterization techniques and promote the fundamental understanding of reaction mechanisms and structure-activity relationships in electrocatalytic energy conversion systems.

Controlling hydrogenation pathway by metal hydride enable efficient electrocatalytic N2 fixation

Electrocatalytic nitrogen fixation under ambient conditions represents an energy-saving sustainable alternative strategy to the energy-consuming traditional Haber–Bosch process toward ammonia synthesis. However, the traditional electrocatalysts for nitrogen reduction reaction (NRR) often suffer low selectivity and low activity. From quantum-mechanical calculations, we obtain a benefit clue that the Ni atom adsorbed by the first hydrogen ion in the catalyst exhibits selectivity for the adsorption of N2 and other H atoms, and it preferentially adsorbs N2 molecules. Thus, we propose an interfacial engineering strategy to simultaneously accelerate selectivity and activity using metal/metal hydroxide. The remarkable activity of metal/metal hydroxide originates from its synergized water dissociation and unique hydrogenation pathway of metal hydride. The priority absorption of the N2 suppresses the competitive hydrogen evolution reaction and accelerates the kinetics to generate ∗N2H: ∗H + N2 → ∗N2H, which a is rate-limiting step for NH3 synthesis. Using Ni/NiFe–OH as prototypes, here we show that selectivity and catalytic activity are simultaneously enhanced, surprisingly, in simple inorganic hybrid and confers exceptionally Faradaic efficiency of 23.34% and NH3 yield 19.74 μg h−1 cm−2 at −0.15 V versus reversible hydrogen electrode (RHE) in 0.5 M KOH electrolyte under ambient conditions. The long-term durability is also excellent. This work provides a possibility for the rational design of efficient electrocatalysts for N2 electrochemical reduction with a large-scale production.

Efficient electrocatalytic overall water splitting and structural evolution of cobalt iron selenide by one-step electrodeposition

Fe-incorporated dual-metal selenide on nickel foam (Co 0.9 Fe 0.1 -Se/NF) with superior and stable electrocatalytic overall water splitting performance in alkaline media is synthesized by a facile one-step electrodeposition method. Developing bifunctional electrocatalysts with both high catalytic activity and high stability is crucial for efficient water splitting in alkaline media. Herein, a Fe-incorporated dual-metal selenide on nickel foam (Co 0.9 Fe 0.1 -Se/NF) is synthesized via a facile one-step electrodeposition method. As-synthesized materials could serve as self-supported bifunctional electrocatalysts with excellent catalytic activity towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. Experimental results show that delivering a 10 mA cm −2 water splitting current density only requires a cell voltage of 1.55 V. In addition, a very stable performance could be kept for about 36 hours, indicating their excellent working stability. Moreover, by means of phase analysis, we have identified that the evolution of the synthesized Co 0.9 Fe 0.1 -Se/NF experiences two entirely different processes in HER and OER, which hydroxide and oxyhydroxide are regarded as the real active sites, respectively. This work may pave the way to further understanding the relationships between the reactivity and stability of chalcogenide-based electrocatalysts and facilitating the rational design of efficient electrocatalysts for future renewable energy system applications.

Design principles of noble metal-free electrocatalysts for hydrogen production in alkaline media: combining theory and experiment

Water electrolysis is a promising solution to convert renewable energy sources to hydrogen as a high-energy-density energy carrier. Although alkaline conditions extend the scope of electrocatalysts beyond precious metal-based materials to earth-abundant materials, the sluggish kinetics of cathodic and anodic reactions (hydrogen and oxygen evolution reactions, respectively) impede the development of practical electrocatalysts that do not use precious metals. This review discusses the rational design of efficient electrocatalysts by exploiting the understanding of alkaline hydrogen evolution reaction and oxygen evolution reaction mechanisms and of the electron structure–activity relationship, as achieved by combining experimental and computational approaches. The enhancement of water splitting not only deals with intrinsic catalytic activity but also includes the aspect of electrical conductivity and stability. Future perspectives to increase the synergy between theory and experiment are also proposed.

Scalable fabrication and active site identification of MOF shell-derived nitrogen-doped carbon hollow frameworks for oxygen reduction

Nitrogen-doped carbon materials as promising oxygen reduction reaction (ORR) electrocatalysts attract great interest in fuel cells and metal-air batteries because of their relatively high activity, high surface area, high conductivity and low cost. To maximize their catalytic efficiency, rational design of efficient electrocatalysts with rich exposed active sites is highly desired. Besides, due to the complexity of nitrogen species, the identification of active nitrogen sites for ORR remains challenging. Herein, we develop a facile and scalable template method to construct high-concentration nitrogen-doped carbon hollow frameworks (NC), and reveal the effect of different nitrogen species on their ORR activity on basis of experimental analysis and theoretical calculations. The formation mechanism is clearly revealed, including low-pressure vapor superassembly of thin zeolitic imidazolate framework (ZIF-8) shell on ZnO templates, in situ carbonization and template removal. The obtained NC-800 displays better ORR activity compared with other NC-700 and NC-900 samples. Our results indicate that the superior ORR activity of NC-800 is mainly attributed to its content balance of three nitrogen species. The graphitic N and pyrrolic N sites are responsible for lowering the working function, while the pyridinic N and pyrrolic N sites as possible active sites are beneficial for increasing the density of states.

Recent advances in rational design of efficient electrocatalyst for full water splitting across all pH conditions

Abstract

Selective electroreduction of CO2 to acetone by single copper atoms anchored on N-doped porous carbon

Efficient electroreduction of CO2 to multi-carbon products is a challenging reaction because of the high energy barriers for CO2 activation and C–C coupling, which can be tuned by designing the metal centers and coordination environments of catalysts. Here, we design single atom copper encapsulated on N-doped porous carbon (Cu-SA/NPC) catalysts for reducing CO2 to multi-carbon products. Acetone is identified as the major product with a Faradaic efficiency of 36.7% and a production rate of 336.1 μg h−1. Density functional theory (DFT) calculations reveal that the coordination of Cu with four pyrrole-N atoms is the main active site and reduces the reaction free energies required for CO2 activation and C–C coupling. The energetically favorable pathways for CH3COCH3 production from CO2 reduction are proposed and the origin of selective acetone formation on Cu-SA/NPC is clarified. This work provides insight into the rational design of efficient electrocatalysts for reducing CO2 to multi-carbon products.

Identifying the role of Ni and Fe in Ni–Fe co-doped orthorhombic CoSe2 for driving enhanced electrocatalytic activity for oxygen evolution reaction

Exploring the origin of high electrocatalytic activity of Ni–Fe–Co ternary selenides for oxygen evolution reaction (OER) is of fundamental importance for rational design of efficient electrocatalysts. In this report, we synthesize self-assembled microspheres by orthorhombic CoSe2 nanorods along with the Ni and/or Fe doped counterparts, and systematically investigate their electrocatalytic performance. The results show that, although either Ni-doping or Fe-doping can significantly enhance the catalytic activity of CoSe2, the ways they promote catalytic activity are different. The Tafel analysis demonstrates that Fe incorporation leads to a kinetics change in the OER while Ni incorporation has little effect. Based on the electrochemical characterizations and theoretical calculations, Ni-doping maintains Co active sites and does not alter the OER mechanism, but decreases the energy barrier of the rate-limiting step by modifying Co active sites. In contrast, Fe-doping transforms the active sites from Co to Fe, and the rate-limiting step changes to the O–OH formation stage, thus affording faster reaction kinetics. These findings are further confirmed by more Ni–Fe co-doped CoSe2 with various content of Ni and Fe. Specifically, under the optimal experimental conditions, Ni–Fe co-doped CoSe2 (Ni0.04Fe0.16Co0.8Se2) exhibits a remarkable OER activity with an overpotential of ∼230 mV at 10 mA cm−2 and Tafel slope of 39 mV dec−1.

Optimizing interfacial electronic coupling with metal oxide to activate inert polyaniline for superior electrocatalytic hydrogen generation

AbstractTuning and optimization of electronic structures and related reaction energetics are critical toward the rational design of efficient electrocatalysts. Herein, experimental and theoretical calculation demonstrate the originally inert N site within polyaniline (PANI) can be activated for hydrogen evolution by proper d‐π interfacial electronic coupling with metal oxide. As a result, the as‐synthesized WO3 assemblies@PANI via a facile redox‐induced assembly and in situ polymerization, exhibits the electrocatalytic production of hydrogen better than other control samples including W18O49@PANI and most of the reported nobel‐metal‐free electrocatalysts, with low overpotential of 74 mV at 10 mA·cm−2 and small Tafel slope of 46 mV·dec−1 in 0.5M H2SO4 (comparable to commercial Pt/C). The general efficacy of this methodology is also validated by extension to other metal oxides such as MoO3 with similar improvements.

Identification of single-atom active sites in carbon-based cobalt catalysts during electrocatalytic hydrogen evolution

Monitoring atomic and electronic structure changes on active sites under realistic working conditions is crucial for the rational design of efficient electrocatalysts. Identification of the active structure during the alkaline hydrogen evolution reaction (HER), which is critical to industrial water–alkali electrolysers, remains elusive and is a field of intense research. Here, by virtue of operando X-ray absorption spectroscopy on a uniform cobalt single-site catalyst, we report the atomic-level identification of the dynamic structure of catalytically active sites under alkaline HER. Our results reveal the formation of a high-valence HO–Co1–N2 moiety by the binding between isolated Co1–N4 sites with electrolyte hydroxide, and further unravel the preferred water adsorption reaction intermediate H2O–(HO–Co1–N2). Theoretical simulations rationalize this structural evolution and demonstrate that the highly oxidized Co sites are responsible for the catalytic performance. These findings suggest the electrochemical susceptibility of active sites, providing a coordination-engineered strategy for the advance of single-site catalysis.

MoS2 nanoparticles coupled to SnS2 nanosheets: The structural and electronic modulation for synergetic electrocatalytic hydrogen evolution

The electrocatalytic hydrogen evolution reaction (HER) is one of the core components of energy conversions. The chemical-physical properties and morphological structures of electrocatalysts are the main factors that determine the HER performance. Thus, the rational design of efficient electrocatalysts is essentially required. A new heteronanostructured system is proposed, which comprises MoS2 nanoparticles (MoS2 NPs) coupled to SnS2 ultrathin nanosheets (SnS2 NS) and operates as an efficient HER electrocatalyst. Advanced spectroscopic techniques are applied to confirm formation of heteronanostructure and occurred electron modulation of MoS2 NPs/SnS2 NS. Surprisingly, the MoS2 NPs/SnS2 NS electrocatalyst is highly efficient for HER with a low overpotential (∼0.249 V at the current density of 10 mA cm−2), small Tafel slope (∼42.1 mV decade−1) and excellent electrocatalytical stability.

Atomic N-coordinated cobalt sites within nanomesh graphene as highly efficient electrocatalysts for triiodide reduction in dye-sensitized solar cells

Facile yet rational design of efficient electrocatalyst toward triiodide reduction reaction is a persistent challenge for the practical application of dye-sensitized solar cell (DSSC). Here we propose a protocol for fabricating atomic N-coordinated cobalt sites (Co-Nx-C) within nanomesh graphene frameworks (Co-NMG). The as-synthesized Co-NMG combines the features of atomically dispersed active sites and interconnected mesoporous structure with high porosity, which makes these active sites fully exposed and accessible while facilitating the mass transport of reactants. As a result, the Co-NMG electrocatalysts with substantial active sites and desired porous architectures exhibit high electrocatalytic activity and long-term electrochemical stability. Electrochemical measurements and DFT calculations reveal that the catalytic sites toward the reduction of triiodide mainly derive from the abundant topological defects, nitrogen dopants, and especially the atomic Co-Nx-C moieties. Furthermore, with Co-NMG as counter electrodes (CEs), the DSSCs display a power conversion efficiency of 9.06%, which is higher than that of Pt CEs (7.71%). This work not only provides a promising CE material for DSSC to address the issues associated with Pt catalyst, but also opens up new avenues for developing nanocarbon based catalysts with desired features for other energy-related applications.

Crossed PtCoCu Alloy Nanocrystals with High‐Index Facets as Highly Active Catalyst for Methanol Oxidation Reaction

AbstractNanocrystals with high‐index facets are arousing growing attention in terms of rational design of efficient electrocatalysts. Herein, ternary PtCoCu alloys with distinct crossed and dendritic structure are prepared via one‐pot approach simply by tuning the amount of serine. The electrocatalytic performances for methanol oxidation reaction by these PtCoCu alloys are examined. It turns out that the {hk0} high‐index facets‐covered surfaces endow the crossed PtCoCu alloy with 4.2‐fold improvement of specific activity relative to commercial Pt/C and with superior stability. This work provides a facile and feasible route for synthesizing tri‐ or multimetallic alloys for electrocatalytic applications.

Plasma-Assisted Synthesis and Surface Modification of Electrode Materials for Renewable Energy.

Renewable energy technology has been considered as a "MUST" option to lower the use of fossil fuels for industry and daily life. Designing critical and sophisticated materials is of great importance in order to realize high-performance energy technology. Typically, efficient synthesis and soft surface modification of nanomaterials are important for energy technology. Therefore, there are increasing demands on the rational design of efficient electrocatalysts or electrode materials, which are the key for scalable and practical electrochemical energy devices. Nevertheless, the development of versatile and cheap strategies is one of the main challenges to achieve the aforementioned goals. Accordingly, plasma technology has recently appeared as an extremely promising alternative for the synthesis and surface modification of nanomaterials for electrochemical devices. Here, the recent progress on the development of nonthermal plasma technology is highlighted for the synthesis and surface modification of advanced electrode materials for renewable energy technology including electrocatalysts for fuel cells, water splitting, metal-air batteries, and electrode materials for batteries and supercapacitors, etc.

Rational design of electrocatalysts and photo(electro)catalysts for nitrogen reduction to ammonia (NH3) under ambient conditions

This perspective highlights the rational design of efficient electrocatalysts and photo(electro)catalysts for N2 reduction to ammonia (NH3) under ambient conditions.

Ultrathin AgPt alloy nanowires as a high-performance electrocatalyst for formic acid oxidation

To address the insufficient electrocatalytic activity and stability of formic acid oxidation reaction (FAOR) electrocatalysts, as well as their high cost, we herein demonstrate the facile hydrothermal synthesis of ultrathin AgPt alloy nanowires using amine-terminated poly(N-isopropylacrylamide) (PNIPAM-NH2) as a structure-directing agent. The initial generation of AgCl precipitates, subsequent formation of AgPt nanoparticles, and their oriented attachment account for the formation of ultrathin AgPt alloy nanowires. Benefiting from their unique 1D anisotropy and alloyed composition, the prepared ultrathin AgPt nanowires exhibit a superior electrocatalytic activity and better CO tolerance for the FAOR, reaching a 1.6-fold and 3.7-fold higher specific current density than AgPt nanoparticles and a commercial Pt black catalyst, respectively. Additionally, the ultrathin AgPt alloy nanowires manifest a superior electrochemical stability and structural robustness during electrocatalysis, making them a promising FAOR electrocatalyst. This work not only provides a reliable strategy for the synthesis of noble metal-based ultrathin nanowires, but also opens an avenue towards the rational design of efficient electrocatalysts for fuel cell systems.