Electrocatalytic Materials Research Articles

Thermally-Activated Cobalt Hexacyanocobaltate Dispersed on Reduced-Graphene-Oxide As Electrocatalyst Towards Oxygen Reduction in an Alkaline Medium

In the recent research years is observed huge interest in design of new functional nanomaterials for developing new electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. The research has been focused on developing carbon nanostructures materials with the different transition metals (e.g. Co, Ni, Ag, Au, Cu, Mn) analogue of polynuclear Prussian Blue for fuel cell applications. The development of electrocatalytic material prepared by heat-treating a composite of a Prussian Blue analogue - cobalt hexacyanocobaltate immobilized on a reduced graphene oxide. The pyrolysis process, forms a new type of catalyst with efficient active cobalt centers (Co-N-C and Co-C-N) of electrochemical oxygen reduction reaction in alkaline media. Physicochemical properties of this catalytic material containing cobalt in differing oxidation states were elucidated using microscopic, spectroscopic methods and various electrochemical diagnostic techniques. Experimental results showed that the cobalt analogue of Prussian Blue displayed comparable electrocatalytic activity (e.g., a half-wave potential and overpotential) towards oxygen reduction reaction in alkaline media to Vulcan-supported platinum nanoparticles. Furthermore, the presence of cyanide-bridged cobalt ionic sites tended to decrease formation of undesirable peroxide intermediate species, as demonstrated by monitoring ring currents during RRDE measurements. Furthermore, the proposed electrocatalytic material exhibits great stability and tolerance to alcohols (e.g. methanol). Acknowledgement The study was supported by the National Science Center (NCN), Poland, Project Number 2015/19/B/ST4/03758

Opportunities and Challenges of Black Phosphorus for Electrocatalysis and Rechargeable Batteries

AbstractAs an emerging 2D layered material, black phosphorus (BP) has received intensive attention in recent years, particularly in electrocatalysis and rechargeable batteries. With further structural modifications, BP‐based heterostructured composites have exhibited attractive physical and chemical properties regarding to enhanced conductivity, ion transport, and catalysis activity, endowing them as potential candidates for electrochemical ions storage and electro/chemical catalysis. In this perspective, a brief summary is first given on the recent progress of BP and BP‐derived materials in electrocatalysis, such as hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and nitrogen reduction reaction (NRR), and in rechargeable batteries, such as lithium‐ion batteries (LIBs), sodium‐ion batteries (SIBs), and potassium‐ion batteries (PIBs), followed by a critical review on the current opportunities and challenges. It is expected that this class of emerging materials will bring about new potential solutions to address the current energy crisis and inspire researchers to develop more novel materials toward future multifunctional applications.

Recent research progress on high-entropy alloys as electrocatalytic materials

High-entropy alloys (HEAs), that are composed of more than five metal elements in almost equimolar ratios, have gained considerable interest as electrocatalytic materials because of their high catalytic activity, high porosity, and excellent stability. HEAs have controllable electronic structures and geometric configurations, which give the prepared materials an unexpected catalytic activity. This review focuses on introducing the research progress on HEAs in recent years and analyses and summarises the new preparation methods, catalytic properties, and theoretical research on the materials. In addition, the opportunities for and challenges faced by HEAs as electrocatalysts are presented. • Covers the preparation methods and feasibility analysis of the HEA nanocatalysts. • No perfect method for industrial preparation of HEA; more scientific studies needed. • Preparation of inexpensive HER catalysts has attracted widespread attention. • Unique structural properties of HEAs improve catalytic performance and reduce costs. • ORR slow kinetics is a key problem to apply fuel cells and metal-oxygen batteries.

A hollow Co0.12Ni1.88S2/NiO heterostructure that synergistically facilitates lithium polysulfide adsorption and conversion for lithium-sulfur batteries

• An ingenious Co 0.12 Ni 1.88 S 2 /NiO heterostructure with a hollow and semi-open architecture was engineered in situ , which synergistically enhanced lithium polysulfide adsorption and conversion for lithium-sulfur batteries. • The considerable electrochemical impedance variation was observed via in situ EIS measurements, which was proved to be related to the content of soluble LiPSs in the electrolyte. • The mechanisms of the strong affinities between Co 0.12 Ni 1.88 S 2 /NiO and lithium polysulfides, and the catalytic effect were further investigated by theoretical calculations. The significant capacity deterioration and inadequate cycling lifespan that are mainly caused by the undesirable “shuttle effect” and torpid redox kinetics have encumbered the development of practically applicable lithium-sulfur (Li-S) battery technology. Modifying sulfur cathodes with lithium polysulfide (LiPS) adsorptive and electrocatalytic host materials is a promising approach to resolving these issues. Herein, a Co 0.12 Ni 1.88 S 2 /NiO heterostructure, which has multiple merits, is designed and serves as a sulfur host to improve the electrochemical performance of Li-S batteries. Possessing strong LiPS adsorbability and excellent electrocatalytic activity, the heterostructural Co 0.12 Ni 1.88 S 2 /NiO exhibits favorable synergistic effects, which effectively facilitate the anchoring and converting of diffused LiPSs. As a result, the corresponding cell delivers rapid redox kinetics and higher sulfur utilization. An impressive initial discharge capacity of 1424.8 mAh g −1 and a reversible capacity near 1056.7 mAh g −1 at 1 C over 1000 cycles are achieved with an average Coulombic efficiency of 98.8%. Benefiting from the unique nanoarchitecture and superior catalytic efficiency, only a very small amount of Co 0.12 Ni 1.88 S 2 /NiO (∼7 wt% in the cathode) is used as the sulfur host. The rational design of Co 0.12 Ni 1.88 S 2 /NiO in this work will hopefully offer inspiration for exploring advanced heterostructure materials for Li-S batteries and other electrochemical devices. Heterostructural Co 0.12 Ni 1.88 S 2 /NiO was engineered as a sulfur host for lithium-sulfur batteries. The catalytic effect and strong LiPS adsorbability synergistically promoted redox kinetics and LiPS conversion, which significantly improved the sulfur utilization during the charging and discharging processes.

Selected applications of operando Raman spectroscopy in electrocatalysis research

Knowledge-guided improvement of electrocatalytic materials is facilitated by insight in determinants of activity, selectivity, and stability. Catalyst re-construction, surface adsorbates and reaction intermediates, and the mechanistic role of the electrolyte can be addressed by operando (= in situ) Raman spectroscopy, where Raman scattering is detected during electrochemical operation. After outlining the basic experimental technology and addressing the light-damage problem, selected applications in electrocatalysis research are reviewed: (1) Redox-state changes of the catalyst material induced by electrode potentials are traced by operando Raman spectroscopy. (2) Surface-bound (adsorbed) educt, products and reaction intermediates are detected using surface-enhanced Raman spectroscopy (SERS). (3) Local-pH values are determined at the catalyst–electrolyte interface, with spatial resolution at the visible-light diffraction limit.

Strategic tailored design of electrocatalysts for environmental remediation based on density functional theory (DFT) and microkinetic modeling

Environmental electrocatalysis has a wide range of applications at the water-energy nexus and will play a key role in mitigating climate change. Performance and selectivity of electrochemical processes are driven by specific electrocatalyst interactions with electroactive species and by-products. Research advances and competitive translation to higher technology readiness levels depend on the identification of suitable electrocatalytic materials. Theoretical modeling can guide electrocatalyst discovery, engineering, and design, which can overturn typical trial-and-error approaches for material discovery in favor of a hypothesis-driven and strategic tailored synthesis approach to electrocatalysts development. In this current opinion, we present an overview of some of the virtues of density functional theory and microkinetic modeling as tools for reinforcing our understanding of complex charge transfer processes in environmental electrochemistry. • Density functional theory strengthens knowledge for electrocatalysts design. • Theoretical models explain thermodynamics and kinetic of electrochemical reactions. • Theoretical models can tailor design of catalyst based on composition. • Theoretical models can identify the most active and selective crystalline facets. • Models still need further development to fully describe electrochemical reactions.

Modifying properties and endurance of CoP by cerium doping to enhances overall water splitting in alkaline medium

The development of efficient electrocatalyst is one of the effective ways to speed up the efficiency of water electrolysis. In this work, we prepared a nested-like Ce-doped CoP nanowires catalytic material on carbon cloth by simple hydrothermal and phosphating methods. After adjusting the doping ratio of Ce, the doping ratio (Ce/W = 6 %) with the best performance is obtained and named as Ce-CoP NWs/CC. The Ce-CoP NWs/CC exhibits preeminent electrocatalytic activity with low overpotentials with 80 and 290 mV at 10 mA cm−2 for HER and OER, respectively. Moreover, the Ce-CoP NWs/CC electrocatalyst also exhibits excellent electrochemical performance in overall water splitting with a low voltage of 1.506 V at 10 mA cm−2, outperforming many reported electrocatalysts. This work provides a feasible electrocatalytic material for the introduction of rare earth elements into water electrolysis.

Flower-like Co3O4@NiFe-LDH nanosheets enable high-performance bifunctionality towards both electrocatalytic HER and OER in alkaline solution

Exploring highly active and cost-effective metal-based overall water splitting catalysts are crucial for the large-scale conversion of sustainable electrical energy to fuels, feedstocks and green economy. Here, a nickel foam-supported electrocatalyst consisting of a one-dimensional Co3O4 nanowire and two-dimensional NiFe-LDH nanosheets is reported. The optimized Co3O4@NiFe-LDH/NF catalyst affords 79 and 215 mV at 10 mA cm−2 for catalyzing the hydrogen and oxygen evolution reaction in 1.0 M KOH, which also exhibits quick reaction kinetics and excellent durability. The self-supported electrode only requires 1.58 V to afford 10 mA cm−2 with astonishing stability for water splitting. The linked interfacial nanostructure between NiFe-LDH and Co3O4, which supports the enhancement of the electronic structure and increases catalytic active sites, is primarily responsible for the electrode’s remarkable catalysis performance. The Co3O4@NiFe-LDH/NF as an ideal electrocatalyst lays forth a broad technique for synthesizing electrocatalytic materials for efficient and scalable water splitting.

Design Strategies and in situ Infrared, Raman, and X‐ray Absorption Spectroscopy Techniques Insight into the Electrocatalysts of Hydrogen Energy System

The challenging sluggish reaction kinetics of hydrogen energy‐related electrocatalysis can be overcome via exploring electrocatalysts with high‐efficient activity and long‐term durability. However, the deficiency of comprehensive and in‐depth understanding of the evolution of the electrocatalysts, nature of active centers, intermediate species absorbed in the electrocatalysts, and the reaction pathway during the electrocatalytic processes seriously limits the elucidation of the composition/structure–activity relationship of electrocatalysts. To this end, plenty of powerful in situ techniques that can provide atomic/molecular information are employed to bridge the understanding of fundamental mechanisms to the practical development of electrocatalysts. This review summarizes design strategies based on composition regulation and morphology design for tuning the electronic/geometric structures of electrocatalytic materials with improved activity and stability. Moreover, the recent application of in situ infrared, Raman, and X‐ray absorption spectroscopy is elaborated with emphases on tracking the dynamic evolution during electrocatalysis and building a link between the composition/structure and activity of electrocatalysts. Finally, the current challenges and future perspectives for in situ monitoring techniques to gain an understanding more deeply and comprehensively in the hydrogen energy‐related electrocatalysis are proposed. This review provides insights into the rational optimization of electrocatalysts and inspire the unraveling mechanism of the enhanced electrocatalytic performance in future research.

Boosting Electrocatalytic Reduction of CO2 to HCOOH on Ni Single Atom Anchored WTe2 Monolayer.

Achieving efficient conversion of carbon dioxide (CO2 ) to formic acid (HCOOH) at mild conditions is a promising means to reduce greenhouse gas emission and mitigate the energy crisis. Herein, spin-polarized density functional theory calculations with van der Waals corrections (DFT+D3) are performed to analyze the catalytic activity of seven metals (Ti, Fe, Ni, Cu, Zn, In, and Sn) anchored on a tungsten ditelluride monolayer (M@WTe2 ) and screen favorable CO2 reduction pathways. These results demonstrate that Ni single atoms strongly bind to the WTe2 monolayer and exist in isolated form due to the high diffusion barriers. Also, Ni-anchored WTe2 monolayer (Ni@WTe2 ) possesses a considerably low limiting-potential (-0.11V vs reversible hydrogen electrode) to convert CO2 to HCOOH due to moderate OCHO adsorption energy and a suppressed competing hydrogen evolution reaction (HER). Therefore, Ni@WTe2 monolayer is a promising electrocatalytic material for the CO2 reduction reaction (CO2 RR). This study sheds light on strategies of designing single metal atom anchored WTe2 catalysts for improved CO2 RR performances.

Achieving Sustainable Development Goal 6 Electrochemical-Based Solution for Treating Groundwater Polluted by Fuel Station

Oil leakage occurs at fuel service stations due to improper storage, which pollutes soil and, subsequently, can reach the groundwater. Many compounds of petroleum-derived fuels pose hazards to aquatic systems, and so must be treated to guarantee clean and safe consumption, which is a right proposed by the United Nations in their Sustainable Development Goal 6 (SDG 6: Clean Water and Sanitation). In this study, contaminated groundwater with emerging pollutants by petroleum-derived fuel was electrochemically treated in constantly mixed 0.5 L samples using three different anodes: Ni/BDD, Ti/Pt, Ti/RuO2. Parameters were investigated according to chemical oxygen demand (COD), energy consumption analysis, by applying different electrodes, current densities (j), time, and the use of Na2SO4 as an electrolyte. Despite a similar COD decrease, better degradation was achieved after 240 min of electrochemical treatment at Ti/RuO2 system (almost 70%) by applying 30 mA cm−2, even without electrolyte. Furthermore, energy consumption was lower with the RuO2 anode, and greater when 0.5 M of Na2SO4 was added; while the order, when compared with the other electrocatalytic materials, was Ti/RuO2 > Ti/Pt > Ni/BDD. Thereafter, aiming to verify the viability of treatment at a large scale, a pilot flow plant with a capacity of 5 L was used, with a double-sided Ti/RuO2 as the anode, and two stainless steel cathodes. The optimal conditions for the effective treatment of the polluted water were a j of 30 mA cm−2, and 0.5 M of Na2SO4, resulting in 68% degradation after 300 min, with almost complete removal of BTEX compounds (benzene, toluene, ethyl-benzene, and xylene, which are found in emerging pollutants) from the water and other toxic compounds. These significant results proved that the technology used here could be an effective SDG 6 electrochemical-based solution for the treatment of groundwater, seeking to improve the quality of water, removing contaminants, and focusing on Brazilian environmental legislations and, consequently, converting pollutants into effluent that can be returned to the water cycle.

Environmental application of a cost-effective smartphone-based method for COD analysis: Applicability in the electrochemical treatment of real wastewater

This study aims to develop a cheap method for the evaluation of quality of water or the assessment of the treatment of water by chemical oxygen demand (COD) measurements throughout the use of the HSV color model in digital devices. A free application installed on a smartphone was used for analyzing the images in which the colors were acquired before to be quantified. The proposed method was also validated by the standard and spectrophotometric methods, demonstrating that no significant statistical differences were attained (average accuracy of 97 %). With these results, the utilization of this smartphone-based method for COD analysis was used/evaluated, for first time, by treating electrochemically a real water matrix with substantial organic and salts content using BDD and Pt/Ti anodes. Aiming to understand the performance of both anodes, bulk experiments were performed under real pH by applying current densities (j) of 15, 30, and 60 mA cm−2. COD abatement results (which were achieved with this novel smart water security solution) clearly showed that different organic matter removal efficiencies were achieved, depending on the electrocatalytic material used as well as the applied current density (42 %, 45 %, and 85 % for Ti/Pt while 93 %, 97 % and total degradation for BDD by applying 15, 30, and 60 mA cm−2, respectively). However, when the persulfate-mediated oxidation approach was used, with the addition of 2 or 4 g Na2SO4 L−1, COD removal efficiencies were enhanced, obtaining total degradation with 4 g Na2SO4 L−1 and by applying 15 mA cm−2. Finally, this smartphone imaging-based method provides a simple and rapid method for the evaluation of COD during the use of electrochemical remediation technology, developing and decentralizing analytics technologies for smart water solutions which play a key role in achieving the Sustainable Development Goal 6 (SDG6).

Tailoring 3D-Printed Electrodes for Enhanced Water Splitting.

Alkaline water electrolysis, a promising technology for clean energy storage, is constrained by extrinsic factors in addition to intrinsic electrocatalytic activity. To begin to compare between catalytic materials for electrolysis applications, these extrinsic factors must first be understood and controlled. Here, we modify extrinsic electrode properties and study the effects of bubble release to examine how the electrode and surface design impact the performance of water electrolysis. We fabricate robust and cost-effective electrodes through a sequential three-dimensional (3D) printing and metal deposition procedure. Through a systematic assessment of the deposition procedure, we confirm the close relationship between extrinsic electrode properties (i.e., wettability, surface roughness, and electrochemically active surface area) and electrochemical performance. Modifying the electrode geometry, size, and electrolyte flow rate results in an overpotential decrease and different bubble diameters and lifetimes for the hydrogen (HER) and oxygen evolution reactions (OER). Hence, we demonstrate the essential role of the electrode architecture and forced electrolyte convection on bubble release. Additionally, we confirm the suitability of ordered, Ni-coated 3D porous structures by evaluating the HER/OER performance, bubble dissipation, and long-term stability. Finally, we utilize the 3D porous electrode as a support for studying a benchmark NiFe electrocatalyst, confirming the robustness and effectiveness of 3D-printed electrodes for testing electrocatalytic materials while extrinsic properties are precisely controlled. Overall, we demonstrate that tailoring electrode architectures and surface properties result in precise tuning of extrinsic electrode properties, providing more reproducible and comparable conditions for testing the efficiency of electrode materials for water electrolysis.

Emerging Heterogeneous Supports for Efficient Electrocatalysis.

Electrocatalysis plays a fundamental role in many fields, such as metallurgy, medicine, chemical industry, and energy conversion. Anchoring active electrocatalysts with controllable loading and uniform dispersion onto suitable supports has become an attractive topic. This is because the supports can not only have the potential to improve catalytic activity and stability through the interaction between support and catalytic center, but also can reduce precious metal consumption by improving atomic utilization. Herein, recent theoretical and experimental progresses concerning the development of supports to anchor electrocatalytic materials are first reviewed. Next, their controllable syntheses, characterization techniques, metal-support electronic interactions, and structure-performance relationships are presented. Some representative carbon supports and non-carbonaceous supports, as well as recently reported star supports such as 2D supports, single atom catalysts, and self-supported catalysts are also summarized. In addition, the significant role of support in stabilizing and regulating catalytic active sites is particularly emphasized. Finally, challenges, opportunities, key problems, and further promising solutions for supported catalysts are proposed.

Effect of Co-Fe alloy nanoparticles on the surface electronic structure of molybdenum disulfide nanosheets and its application as a bifunctional catalyst for rechargeable zinc air battery

It is of great significance to improve the performance of electrocatalysts by constructing suitable heterogeneous interfaces to adjust the electronic structure of their surfaces. Here, we design and synthesize Co-Fe alloy nanoparticles (NPs) modified nitrogen-doped cubic carbon box (NC) supported MoS 2 nanosheets (NC@MoS 2 @Co-Fe) as a bi-functional electrocatalytic electrode material, which possesses excellent electrocatalytic oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) performance. The NC@MoS 2 @Co-Fe exhibits remarkable bifunctional electrocatalytic activities with an ORR half-wave potential of 0.73 V in 0.1 M KOH electrolyte and an OER overpotential of 400 mV, driving a current density of 10 mA cm −2 . The advanced catalytic performance can be attributed to the unique heterojunction structure of the catalyst. The size of the Co-Fe alloy NPs supported on MoS 2 can be tuned to avoid the excessive growth of alloy NPs and to expose more catalytic active sites. Meanwhile, the loaded Co-Fe alloy NPs should be covered with a calcined carbon layer derived from the organic ligand to prevent oxidation passivation and particle aggregation. The structure formed by Co-Fe alloy NPs and NC@MoS 2 optimizes the electronic structure of the active center and accelerates the electrocatalytic reaction rate, thus synergistically improving the bi-functional electrocatalytic activity of the NC@MoS 2 @Co-Fe catalyst and can be applied to rechargeable zinc air batteries. Co-Fe alloy nanoparticles (NPs) modified nitrogen-doped cubic carbon box (NC) supported MoS 2 nanosheets (NC@MoS 2 @Co-Fe) is synthesized as a bi-functional electrocatalytic electrode material, which possesses excellent electrocatalytic oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) performance. • The NC@MoS 2 @Co-Fe exhibits remarkable bi-functional electrocatalytic activities. • The assembled Zn-air batterie delivers a high power density and superior cycling performance. • The precise control of Co-Fe alloy on the surface electronic structure is realized. • The hollow nitrogen doped carbon box has a good electrolyte diffusion channel. • The unique MoS 2 @Co-Fe heterojunction structure optimizes the electronic structure of the active center.

Fabrication of amorphous PdNiCuP nanoparticles as efficient bifunctional and highly durable electrocatalyst for methanol and formic acid oxidation

• We utilize a facile laser liquid ablation method to synthesize amorphous PdNiCuP. • The amorphous PdNiCuP is highly efficient and stable for both MOR and FAOR. • The amorphous PdNiCuP displays superior anti-poisoning ability. Highly active and durable electrocatalytic materials towards small molecules electro-oxidation reaction are critical to the large-scale commercial applications of direct liquid fuel cells. Unfortunately, current nanocrystalline electrocatalysts normally suffer from low catalytic efficiency, severe CO poisoning and rapid activity decay. Herein, we report a novel amorphous PdNiCuP catalyst synthesized with laser liquid ablation as a potential settlement to this issue. The as-obtained amorphous PdNiCuP catalyst exhibits enhanced electrocatalytic performance with the mass activity of 1.61 A mg −1 and 737.8 mA mg −1 towards methanol oxidation reaction (MOR) and formic acid oxidation reaction (FAOR), respectively. Moreover, amorphous PdNiCuP displays excellent operation stability and CO-poisoning resistance in both alkaline and acidic medium. P was proposed to play the decisive role for forming the amorphous structure and maintaining the catalytic stability in MOR and FAOR processes. This work provided insights for the ration design of active and durable amorphous electrocatalysts applied in direct liquid fuel cells.

Proton conduction and electrochemical enzyme-free glucose sensitive sensing based on a newly constructed Co-MOF and its composite with hydroxyl carbon nanotubes

It is a great challenge to construct MOFs-based materials with low activation energy for potential applications in proton exchange membrane fuel cells (PEMFCs) as well as fine electrocatalytic glucose sensing performance. Herein, we report a novel 2D Co-MOF {[Co(iip)(bbbm)(H2O)2]·2DMF·2H2O}n obtained through the assembly between Co(II) and 5-iodoisophthalic acid (H2iip) in the presence of the hydrophobic ligand 1,1-(1,4-butanediyl)bis-1H-benzimidazole (bbbm). Its composite with hydroxyl-functionalized carbon nanotubes (Co-MOF@CNTs) was fabricated under ambient conditions. The (8) hydrogen-bonded ring exists in Co-MOF. Both the composite membranes of Co-MOF and Co-MOF@CNTs with nafion exhibit interesting proton-conductive behavior, which are even superior to that of nafion in aqueous medium with the same pH values. Among them, the proton conductivity of the composite Co-MOF@CNTs/nafion membrane is expectedly superior to that of the composite Co-MOF/nafion membrane. Remarkably, the composite Co-MOF@CNTs/nafion membrane exhibited an exceptionally low activation energy (Ea = 0.082 eV, pH = 3), which is among one of the lowest Ea values for the reported novel proton-conducting polymeric materials/composites, resulting in almost unchanged conductivity over the measured temperature range, revealing its potential application in PEMFCs. Moreover, both the pristine Co-MOF and its composite Co-MOF@CNTs could serve as electrocatalytic materials toward glucose oxidation. The Co-MOF@CNTs electrode exhibits expectedly more rapid and sensitive electrochemical glucose sensing with relatively lower determination limit (LOD = 3 μM) and larger detection range (0.01–5 mM) in comparison with that of the pristine Co-MOF (LOD = 0.021 mM, 0.01–2.40 mM).

Tunable Structured MXenes With Modulated Atomic Environments: A Powerful New Platform for Electrocatalytic Energy Conversion.

Owing to their rich surface chemistry, high conductivity, tunable bandgap, and thermal stability, structured 2D transition-metal carbides, nitrides, and carbonitrides (MXenes) with modulated atomic environments have emerged as efficient electrochemical energy conversion systems in the past decade. Herein, the most recent advances in the engineering of tunable structured MXenes as a powerful new platform for electrocatalytic energy conversion are comprehensively summarized. First, the state-of-the-art synthetic and processing methods, tunable nanostructures, electronic properties, and modulation principles of engineering MXene-derived nanoarchitectures are focused on. The current breakthroughs in the design of catalytic centers, atomic environments, and the corresponding structure-performance correlations, including termination engineering, heteroatom doping, defect engineering, heterojunctions, and alloying, are discussed. Furthermore, representative electrocatalytic applications of structured MXenes in energy conversion systems are also summarized. Finally, the challenges in and prospects for constructing MXene-based electrocatalytic materials are also discussed. This review provides a leading-edge understanding of the engineering of various MXene-based electrocatalysts and offers theoretical and experimental guidance for prospective studies, thereby promoting the practical applications of tunable structured MXenes in electrocatalytic energy conversion systems.

Diamondized carbon nanoarchitectures as electrocatalytic material for sulfate-based oxidizing species electrogeneration

The introduction of nanotechnology seems to be an imperative factor to intensify the synergic effects of electrocatalytic materials to produce strong oxidant species or to increase the active sites on their surfaces as well as to enhance the conversion yield in a fuel cell, high-added value products, electrolytic treatment for environmental protection or the detection limit in electroanalysis. Recently, a new type of 3D-diamond electrodes was developed with boron-doped carbon nanowalls (B:CNW), which was manufactured using the microwave plasma-assisted chemical vapor deposition (CVD) process, improving the charge transfer and enhancing the electrochemical performance. The applicability of a BDD/boron-doped carbon nanowalls (BDD/B:CNW) anodes to degrade organic pollutants has been already investigated; however, no attempts at the electrosynthesis of oxidizing species using these diamond-carbon nanostructures have been reported yet. Therefore, the electrosynthesis of sulfate-based oxidizing species was studied here to answer relevant questions from both fundamental and practical point-of-view. The results demonstrated that persulfate was efficiently produced at the BBD electrode, while that the ion-radical sulfate could be the most important oxidant at BDD/B:CNW anode when compared to other electrocatalytic materials, including BDD surfaces. Persulfate concentrations ranged from 3 to 6 µM, depending on the applied current density (2.5, 5.0, and 15 mA cm−2), at diamond electrodes. A dye-model pollutant - methyl orange (MO) was degraded below the limit of detection within 45 min using BDD/B:CNW when in-situ sulfate-based oxidizing species were electrogenerated. These kinds of 3D-diamond-carbon nanostructures are thus promising as novel electrocatalyst for various catalytic applications in the environmental and energy fields.

Pd-Supported Co3O4/C Catalysts as Promising Electrocatalytic Materials for Oxygen Reduction Reaction

This paper describes the activity of PdCo3O4/C obtained by wet impregnation towards the oxygen reduction reaction (ORR). For this purpose, the Co3O4/C substrate was synthesized using the microwave irradiation heating method with further annealing of the substrate at 400 °C for 3 h (Co3O4/C-T). Then, the initial Co3O4/C substrate was impregnated with palladium chloride (Pd-Cl2-Co3O4/C), and then part of the obtained Pd-Cl2-Co3O4/C catalyst was annealed at 400 °C for 3 h (PdOCo3O4/C). The electrocatalytic activity of the prepared catalysts was investigated for the oxygen reduction reaction in alkaline media and compared with the commercial Pt/C (Tanaka wt. 46.6% Pt) catalyst. It was found that the annealed PdOCo3O4/C catalyst showed the largest ORR current density value of −11.27 mA cm−2 compared with Pd-Cl2-Co3O4/C (−7.39 mA cm−2) and commercial Pt/C (−5.25 mA cm−2).