Preparation Of Electrocatalysts Research Articles

Dynamic hydrogen bubble template electrodeposition of Ru on amorphous Co support for electrochemical hydrogen evolution

Electrolyzing water is an environmentally friendly and renewable way to obtain high purity hydrogen. Ruthenium has strong water dissociation ability and suitable hydrogen adsorption energy, so it is considered as one of the candidates of excellent electrocatalysts for hydrogen evolution in alkaline solution. The dynamic hydrogen bubble template (DHBT) is a good electrodeposition technology, which can obtain the 3D metal foams. However, as far as we know, there is no report on the preparation of Ru electrocatalyst by the DBHT method. In this work, the trumpet-shaped Ru on amorphous cobalt support (T-Ru/a-Co) is prepared by the DHBT electrodeposition for the first time. The defect locations are uniformly distributed on the surface of amorphous cobalt (a-Co), which can effectively lead to the formation of nano-bubble template in the DHBT process. However, this special morphology cannot be obtained on the surface of crystalline Co (c-Co). In addition, the electronic structure of T-Ru/a-Co has also been obviously modified, in which the proportion of Ru4+/Ru0 in T-Ru/a-Co has increased, accompanied by the change of binding energy of Ru. It only needs an overpotential of 49 mV to obtain a current density of 10 mA cm−2 for the T-Ru/a-Co. The specific activity (SA), turnover frequency (TOF) and mass activity (MA) of T-Ru/a-Co are 0.23 mA cm−2, 0.48 s−1 and 0.24 A mg−1, which are both higher than those of Pt/C, the disk-shaped Ru on the c-Co support (D-Ru/c-Co) and Ru/C, respectively.

Stable CuIn alloy for electrochemical CO2 reduction to CO with high-selectivity

High-selective and stable electrocatalysts are highly desired for CO2 reduction in large scale. To achieve CO2 reduction to CO with high selectivity and longtime running stability, CuIn alloy nanowires (NWs) is prepared by the combining of chemical oxidation and electrodeposition method. More importantly, due to electrochemical pretreatment during synthesis process, the CuIn alloy shows remarkable stability and its structure remains unchanged under harsh negative bias during CO2 reduction. In addition, the alloy NWs achieve the optimal CO2 to CO selectivity with a Faradaic efficiency of 86% at −1.0 V vs. RHE. Through DFT calculation, it is found that the stable CuIn alloy surface is crucial for the modulation of *COOH intermediate bonding to catalyst for easier formation of *CO, and the *CO dimerization is inhibited by CuIn alloy surface due to the weaker *CO adsorption compared to metallic Cu. We believe this work will shed light on the preparation of stable electrocatalysts for CO2 reduction with high selectivity, and deep understanding of metal surface evolution under electrochemical environment.

Facile fabrication of Sn/SnOx electrode as an efficient electrocatalyst for CO2 reduction to formate

Producing valuable hydrocarbons via electrochemical reduction of CO2 has been a promising active research area. In this study, it was aimed to develop a low-cost and efficient Sn-based electrode reducing CO2 to formate with high selectivity. SnOx thin-film electrode was prepared via potentiostatic electrodeposition at the potentials of −0.5 V, −0.6 V, −0.7 V, and −0.8 V vs. Ag/AgCl on a pure Sn plate for 300 s in an acidic media. The Sn/SnOx electrode which was prepared at −0.6 V was found to have the highest Faradaic efficiency. Electrochemical reduction of CO2 was carried out on this Sn/SnOx electrode in aqueous CO2-saturated 0.1 M KHCO3 solution. The optimum values for the parameters which have significant impacts on Faradaic efficiency for producing formate namely, electrolysis potential and electrolysis time were determined. The maximum Faradaic efficiency of formate on the Sn/SnOx electrode was obtained as 74.7 % at the applied potential of −1.8 V in an H-type cell. The maximum Faradaic efficiency of formate obtained on the Sn/SnOx electrode reached about twice the value obtained on the Sn plate (39.7 %). The results also indicated that the Sn/SnOx electrode has higher catalytic stability and electrochemically active surface area (2.08 cm2) than the bare Sn plate (0.82 cm2). This study showed that an efficient Sn/SnOx electrode can be developed with a simple method that involves only a SnSO4/H2SO4 solution and as short as 300 s plating duration via electrodeposition at a lower overpotential of −0.6 V. The novelty of this study can be attributed to the combination of simple and unique electrocatalyst preparation procedure with less energy consumption and chemical/additive use, short deposition time, and relatively low overpotential for developing an efficient Sn/SnOx electrocatalyst ensuring a high Faradaic efficiency for formate production. Thus, producing formate from the conversion of CO2 which is a waste carbon source, was achieved by a quite simple and economic method.

Metal nanoparticles capped with plant polyphenol for oxygen reduction electrocatalysis

The development of a convenient and universal strategy for the synthesis of inorganic–organic hybrid nanomaterials with phenolic coating on the surface is of special significance for the preparation of electrocatalysts. In this work, we report an environmentally friendly, practical, and convenient method for one-step reduction and generation of organically capped nanocatalysts using natural polyphenol tannic acid (TA) as reducing agents and coating agents. TA coated metal (Pd, Ag and Au) nanoparticles are prepared by this strategy, among which TA coated Pd nanoparticles (PdTA NPs) show excellent oxygen reduction reaction activity and stability under alkaline conditions. Interestingly, the TA in the outer layer makes PdTA NPs methanol resistant, and TA acts as molecular armor against CO poisoning. We propose an efficient interfacial coordination coating strategy, which opens up new way to regulate the interface engineering of electrocatalysts reasonably and has broad application prospects.

Plasma Electrolytic Oxidation of Titanium in Ni and Cu Hydroxide Suspensions towards Preparation of Electrocatalysts for Urea Oxidation

The increasing climate crisis requires an improvement in renewable energy technologies. One of them are fuel cells, devices that are capable of generating electricity directly from the chemical reaction that is taking place inside of them. Despite the advantages of these solutions, a lack of the appropriate materials is holding them back from commercialization. This research shows preliminary results from a simple way to prepare black TiO2 coatings, doped with Cu or Ni using the plasma electrolytic oxidation process, which can be used as anodes in urea-fueled fuel cells. They show activity toward urea oxidation, with a maximum current density of 130 μA cm-2 (@1 V vs. Hg|HgO) observed for Cu-enhanced TiO2 and low potential of only 0.742 V (Vs Hg|HgO) required for 50 μA cm-2 for Ni-enhanced TiO2. These results demonstrate how the PEO process can be used for the preparation of TiO2-based doped materials with electrocatalytic properties toward urea electrooxidation.

A novel 3D CoNiCu-LDH@CuO micro-flowers on copper foam as efficient electrocatalyst for overall water splitting

The superior advantage of electrochemical water splitting for sustainably producing hydrogen has stimulated the rational design and preparation of cost-effective, efficient, and durable bi-functional electrocatalysts. Herein, we present a strategy to fabricate 3D CoNiCu-LDH@CuO heterostructures by a three-step method. With in situ growing Cu(OH)2 nanorod arrays on copper foam, a tri-metallic CoNiCu-BDC MOF with uniform dispersion was formed on the substrate, which can be transferred to a 3D CoNiCu-LDH with a micro-flower structure. The constructed CoNiCu-LDH@CuO/CF self-supporting electrode displays good performance in alkaline media, obtaining low overpotentials of 262 mV and 286 mV at a relatively large current density of 100 mA cm−2 for HER and OER, respectively. Detailed characterizations reveal that the improved HER and OER activity are ascribed to the rich active sites, tight contact between CoNiCu-LDH and substrate, and lower charge-transfer resistance.

Tuning Structures and Microenvironments of Cu-Based Catalysts for Sustainable CO2 and CO Electroreduction

ConspectusThe carbon balance has been disrupted by the widespread use of fossil fuels and subsequent excessive emissions of carbon dioxide (CO2), which has become an increasingly critical environmental challenge for human society. The production and use of renewable energy sources and/or chemicals have been proposed as important strategies to reduce emissions, of which the electrochemical CO2 (or CO) reduction reaction (CO2RR/CORR) in the aqueous systems represents a promising approach.Benefitted by the capacity of manufacturing high-value-added products (e.g., ethylene, ethanol, formic acid, etc.) with a net-zero carbon emission, copper-based CO2RR/CORR powered by sustainable electricity is regarded as a potential candidate for carbon neutrality. However, the diversity of selectivities in copper-based systems poses a great challenge to the research in this field and sets a great obstacle for future industrialization.To date, scientists have revealed that the electrocatalyst design and preparation play a significant role in achieving efficient and selective CO2-to-chemical (or CO-to-chemical) conversion. Although substantial efforts have been dedicated to the catalyst preparation and corresponding electrosynthesis of sustainable chemicals from CO2/CO so far, most of them are still derived from empirical or random searches, which are relatively inefficient and cost-intensive. Most of the mechanism studies have suggested that both intrinsic properties (such as electron states) and extrinsic environmental factors (such as surface energy) of a catalyst can significantly alter catalytic performance. Thus, these two topics are mainly discussed for copper-based catalyst developments in this Account.Here, we provided a concise and comprehensive introduction to the well-established strategies employed for the design of copper-based electrocatalysts for CO2RR/CORR. We used several examples from our research group, as well as representative studies of other research groups in this field during the recent five years, with the perspectives of tuning local electron states, regulating alloy phases, modifying interfacial coverages, and adjusting other interfacial microenvironments (e.g., molecule modification or surface energy). Finally, we employed the techno-economic assessment with a viewpoint on the future application of CO2/CO electroreduction in manufacturing sustainable chemicals. Our study indicates that when carbon price is taken into account, the electrocatalytic CO2-to-chemical conversion can be more market-competitive, and several potential value-added products including formate, methanol, ethylene, and ethanol can all make profits under optimal operating conditions. Moreover, a downstream module employing traditional chemical industrial processes (e.g., thermal polymerization, catalytic hydrolysis, or condensation process) will also make the whole electrolysis system profitable in the future. These design principles, combined with the recent advances in the development of efficient copper-based electrocatalysts, may provide a low-cost and long-lasting catalytic system for a profitable industrial-scale CO2RR in the future.

Construction of Non-Precious Metal Self-Supported Electrocatalysts for Oxygen Evolution from a Low-Temperature Immersion Perspective.

Water splitting is considered as a promising technology to solve energy shortage and environmental pollution. Since oxygen evolution reaction (OER) directly affects the efficiency of hydrogen evolution, the preparation of efficient and inexpensive OER catalysts is an urgent problem. "Low-temperature immersion" (LTI) is expected to be a prospective strategy for electrocatalyst preparation due to its simplicity and energy-saving advantages. However, there is almost no comprehensive overview on the progress of LTI engineering in the construction of non-precious metal self-supported electrocatalysts for OER. Herein, this review firstly introduces the principles and applications of LTI engineering-assisted preparation of non-precious metal self-supported electrocatalysts in terms of etching and deposition. Then the mechanism of OER is analyzed from an amorphous viewpoint, and finally some perspective insights and future challenges of this method are discussed.

Hollow Ni/NiO/C composite derived from metal-organic frameworks as a high-efficiency electrocatalyst for the hydrogen evolution reaction

Metal-organic frameworks (MOFs) constitute a class of crystalline porous materials employed in storage and energy conversion applications. MOFs possess characteristics that render them ideal in the preparation of electrocatalysts, and exhibit excellent performance for the hydrogen evolution reaction (HER). Herein, H–Ni/NiO/C catalysts were synthesized from a Ni-based MOF hollow structure via a two-step process involving carbonization and oxidation. Interestingly, the performance of the H–Ni/NiO/C catalyst was superior to those of H–Ni/C, H–NiO/C, and NH–Ni/NiO/C catalysts for the HER. Notably, H–Ni/NiO/C exhibited the best electrocatalytic activity for the HER, with a low overpotential of 87 mV for 10 mA cm−2 and a Tafel slope of 91.7 mV dec−1. The high performance is ascribed to the synergistic effect of the metal/metal oxide and hollow architecture, which is favorable for breaking the H–OH bond, forming hydrogen atoms, and enabling charge transport. These results indicate that the employed approach is promising for fabricating cost-effective catalysts for hydrogen production in alkaline media.

Facile Preparation of Metallic Sites Anchored Nanocarbon Materials for Electrocatalysis

AbstractHerein, a novel method, heat mechanochemical synthesis (HMCS), is reported for facile and scalable preparation of electrocatalysts with metallic sites anchored on carbon materials. The method simultaneously provides mechanical energy and heat to drive reaction, by which target metal atoms are efficiently trapped in N‐doped and defect‐rich carbon that prepared in advance (NC). The advantages of this method are: (1) high contents of metals at the outermost surface; (2) unique metal sites formed under collisions with mechanical energy; and (3) not annealed at high temperatures, which would retain some unique active sites on the materials. A series of unitary transition metal (Cr, Mn, Fe, Co, Ni, Cu, or Zn) superficially anchored carbons are obtained via the HMCS. More than this, it is quite convenient to prepare multiple metals, such as combinations among these metals, highly dispersed and anchored on the carbon materials in one time. As a representative, the as‐prepared Fe‐NC (denoted as FeNCHM in context) is investigated in detail as catalyst for ORR and Zn‐air battery applications. The authors envision that the method of HMCS provides a good support of surface engineering for preparation of metals sites containing carbon at large scale.

Ta3N5 Nanobelt-Loaded Ru Nanoparticle Hybrids' Electrocatalysis for Hydrogen Evolution in Alkaline Media.

Electrochemical hydrogen evolution is a highly efficient way to produce hydrogen, but since it is limited by high-cost electrocatalysts, the preparation of high-efficiency electrocatalysts with fewer or free noble metals is important. Here, Ta3N5 nanobelt (NB)-loaded Ru nanoparticle (NP) hybrids with various ratios, including 1~10 wt% Ru/Ta3N5, are constructed to electrocatalyze water splitting for a hydrogen evolution reaction (HER) in alkaline media. The results show that 5 wt% Ru/Ta3N5 NBs have good HER properties with an overpotential of 64.6 mV, a Tafel slope of 84.92 mV/dec at 10 mA/cm2 in 1 M of KOH solution, and good stability. The overpotential of the HER is lower than that of Pt/C (20 wt%) at current densities of 26.3 mA/cm2 or more. The morphologies and structures of the materials are characterized by scanning electron microscopy and high-resolution transmission electron microscopy, respectively. X-ray photoelectron energy spectroscopy (XPS) demonstrates that a good HER performance is generated by the synergistic effect and electronic transfer of Ru to Ta3N5. Our electrochemical analyses and theoretical calculations indicate that Ru/Ta3N5 interfaces play an important role as real active sites.

Stainless steel mesh-based CoSe/Ni3Se4 heterostructure for efficient electrocatalytic overall water splitting

The construction of high-efficiency bifunctional electrocatalysts is still a main challenge for hydrogen production from water splitting, in which comprehensive structure regulation plays a key role for synergistically boosting the intrinsic activity and charge collection. Here, we used a two-step hydrothermal method for construction of an interjaculated CoSe/Ni3Se4 heterostructure from NiCo LDH nanosheets grown on stainless steel (SS) meshes as bifunctional electrocatalysts for overall water splitting. The SS meshes containing Fe and Ni act as an excellent 3D scaffold for catalyst growth and charge collection. The SS@CoSe/Ni3Se4 composite exhibits outstanding electrocatalytic performances with low overpotentials of 97 mV for hydrogen evolution and 230 mV for oxygen evolution to reach a current density of 10 mA cm−2, respectively. Moreover, by using SS@CoSe/Ni3Se4 as both the cathode and anode, the assembled electrolyze only required 1.55 V to reach 10 mA cm−2 for overall water splitting. The outstanding performance of SS@CoSe/Ni3Se4 benefits from the synergy between excellent charge collection capability of SS meshes and the abundant active sites at the CoSe/Ni3Se4 heterointerface formed with the in-situ conversion of NiCo LDH nanosheets. Electrochemical active surface area and impedance spectrum indicate that the CoSe/Ni3Se4 loaded on SS has the most abundant electrochemically active sites and the smallest electrochemical resistance, thereby exposing more active sites and enhancing the charge transfer to promote the catalytic activity. By integrating the delicate nanoscale heterostructure engineering with the microscale SS mesh scaffold, our work provides a new perspective for the preparation of high-performance and cheap electrocatalysts that are easy to be integrated with industrial applications.

Boosting electrocatalytic CO2 reduction to formate via carbon nanofiber encapsulated bismuth nanoparticles with ultrahigh mass activity

Electrochemical CO2 conversion is one of the most promising technologies to achieve carbon neutrality. However, it still suffers from some nonnegligible challenges on low production rate and unsatisfied current densities for potential large-scale applications. Herein, we prepare ultrasmall Bi nanoparticles uniformly encapsulated in the carbon nanofibers through electrospinning techniques, which is denoted as Bi/CNFs-900. Gratifyingly, this Bi/CNFs-900 catalyst demonstrates excellent performance and stability on CO2 electro-reduction in a broad potential window. Specifically, it can produce formate with a Faradaic efficiency over 90% and a high partial current density of –235.3 mA cm−2 at −1.23 V vs. RHE in a flow-cell. Furthermore, the confinement effect of carbon nanofibers largely restricts the severe aggregation of bismuth nanoparticles during synthesis as well as electrolysis procedure, which greatly increases the accessible active sites and decreases the actual mass fraction of bismuth composition. Consequently, Bi/CNFs-900 not only achieves ultrahigh mass activity of –1.6 A mgBi−1, but also possesses an unprecedented formate production rate of 4403.3 μmol h−1 cm−2. DFT calculations and in situ Raman spectroscopy further uncover the possible reaction mechanism for CO2 reduction toward formate. These results could provide an economical and industrial-viable strategy for the preparation of electrocatalysts in CO2 reduction.

Single Cobalt Atoms Immobilized on Palladium-Based Nanosheets as 2D Single-Atom Alloy for Efficient Hydrogen Evolution Reaction.

Single-atom alloys (SAAs) display excellent electrocatalytic performance by overcoming the scaling relationships in alloys. However, due to the lack of a unique structure engineering design, it is difficult to obtain SAAs with a high specific surface area to expose more active sites. Herein, single Co atoms are immobilized on Pd metallene (Pdm) support to obtain Co/Pdm through the design of the engineered morphology of Pd, realizing the preparation of ultra-thin 2D SAA. The unsaturated coordination environments combined with the unique geometric and electronic structures realize the modulation of the d-band center and the redistribution of charges, generating highly active electronic states on the surface of Co/Pdm. Benefiting from the synergistic interaction and spillover effect, the Co/Pdm electrocatalyst exhibits outstanding hydrogen evolution reaction (HER) performance in both acid and alkaline solutions, especially with a Tafel slope of 8.2mV dec-1 and a low overpotential of 24.7mV at 10mA cm-2 in the acidic medium, which outperforms commercial Pt/C and Pd/C. This work highlights the successful preparation of 2D ultra-thin SAA, which provides a new strategy for the preparation of HER electrocatalyst with high efficiency, activity, and stability.

Electrocatalytic water splitting by a low crystallinity CeOx@Co3O4 heterostructure

The development of bifunctional electrocatalysts with high activity and low cost is urgent but remains challenging for water splitting. Here, the core–shell heterostructure between ultrasmall ceria nanoparticles with low crystallinity and Co3O4 nanowires (CeOx@Co3O4) is successfully constructed via rapid electrodeposition. Systematic studies revealed that ultrasmall ceria with low crystallinity can induce the rich unsaturated active sites, accelerate the charge transfer and provide the strong electronic interaction between Co3O4 and ceria. As a result, a strong enhancement of electrocatalytic activity at the CeOx@Co3O4 heterostructure is reported with low overpotential (252 and 106 mV at 10 mA cm−2) and small Tafel slopes (41 and 106 mV dec−1) for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The electrolyzer based on CeOx@Co3O4 heterostructure shows a low cell voltage of 1.57 V and excellent stability to attain a current density of 10 mA cm−2. This work provides a valuable reference for the preparation of bifunctional electrocatalysts with low cost and high activity.

The Necessity for Multiscale In Situ Characterization of Tailored Electrocatalyst Nanoparticle Stability

Tailored nanoparticles have opened up several exciting avenues to boost the activity and selectivity of structure-sensitive electrocatalytic reactions, such as the electrochemical carbon dioxide (CO2) reduction (eCO2RR). Colloidal chemistry provides the perfect toolbox to synthesize electrocatalyst nanoparticles on demand with atomic precision, in order to control and steer the electrocatalytic reactions of interest to the desired products. Not only does colloidal chemistry offer a means to prepare nanoparticles with well-defined sizes and shapes, it also allows easy deposition on any desired substrate (e.g., porous substrates) due to the solution processability. But what you see after synthesis with ex situ characterization techniques is not always what you get during the electrocatalytic reaction. Like any other electrocatalyst material, colloidal nanoparticles are prone to restructuring, and hence, the reaction output is altered due to destabilization of the electrocatalyst. This destabilization of the electrocatalyst nanoparticles is currently one of the major bottlenecks for the widespread implementation of electrocatalysts in the chemical industry. This calls for the necessary development and application of in situ characterization techniques to probe the morphology and composition of the tailored electrocatalyst nanoparticles over multiple length scales, in order to rationally design the next generation of stable electrocatalyst nanoparticles. Through detailed spatiotemporal in situ characterization, we can take full advantage of the possibilities that colloidal chemistry offers for electrocatalyst preparation with superior activity, selectivity, and stability. In this perspective, the necessity for in situ characterization of electrocatalyst nanoparticle stability is highlighted. For this purpose, first the progress of colloidal nanoparticles for electrocatalytic conversion reactions is briefly discussed, after which the focus shifts toward in situ characterization of the (in)stability of the tailored nanoparticles during the reaction of interest, ideally under industrially relevant conditions. This perspective shows that in situ characterization of electrocatalyst deactivation requires a multiscale approach, and that without combined in situ characterization we will remain blind to several aspects that are known to influence electrocatalyst performance.

An automatic robot system for machine learning–assisted high-throughput screening of composite electrocatalysts

An automatic robot developed for the high-throughput preparation and characterization of electrocatalysts was used in conjunction with machine learning–aided composition optimization to achieve the selective production of O2/HClO from NaCl solution.

PMo12 induced MoP as hydrogen evolution electrocatalysts

In recent years, electrolytic water has become the mainstream method of producing hydrogen energy, in which the development of efficient electrocatalysts is particularly important. Herein, MoP@C was synthesized by simple hydrothermal following one-step calcination process. MoP@C shows excellent catalytic activity in acidic environment, requiring only a small overpotential (196 mV) at the current density of 10 mA cm-2 and exhibiting a small Tafel slope (91 mV dec-1). Meanwhile, MoP@C displays good stability within 24 hours. This work has a positive effect for the subsequent large-scale preparation of phosphides electrocatalysts.

Nitridation-free preparation of bimetallic oxide-nitride bifunctional electrocatalysts for overall water splitting.

A novel one-pot surfactant-free synthesis is presented for designing bimetallic oxide-nitride electrocatalysts with tunable morphologies using metal salts and nitrogen-rich precursors. This innovative approach eliminates the need for a distinct nitridation process. Bifunctional electrode Co3O4/MoO3/MoxNy achieved a current density of 10 mA cm-2 while maintaining a cell voltage of 1.52 V, outperforming many bimetallic oxide-nitride catalysts in the scientific literature.

Nano-Co-embedded carbon nanofibers for oxygen reduction reaction in Zn-air batteries

The preparation of inexpensive, environmentally friendly, and stable electro-catalysts is crucial for realizing large-scale practical applications of Zn-air batteries. Herein, Co nanoparticles are successfully encapsulated in N-doped carbon nanofibers by electrospinning technique. The obtained material has the characteristics of stable fibrous structure, abundant active centers and fast electron transport. As expected, Co@HPCNFs-800 exhibits high catalytic activity with its initial potential (0.925 V) and onset half-wave potential (0.824 V). Meanwhile, the stability of Co@HPCNFs-800 is significantly higher than commercial Pt/C. Most importantly, the rechargeable Zn-air batteries using Co@HPCNFs-800 catalyst exhibit good open-circuit voltage and cycling stability, demonstrating their potential for practical application. Therefore, this facile method can generally be used to synthesize non-noble metal electrocatalysts to improve energy conversion efficiency.