Ni-based Catalysts Research Articles

Alumina lattice confined Niσ+ species as highly selective and anti-coking sites for sustainable propane dehydrogenation

Propane dehydrogenation (PDH) is a vital petrochemical process. As an alternative to Pt and Cr-based catalysts, Ni-based catalysts used in PDH, however, exhibit low propylene selectivity with severe coking. This work aims to understand the role of different Ni species in PDH and achieve high propylene selectivity by inhibiting coking. Specifically, we obtained NiOx/Al2O3 catalysts with solely tetrahedrally coordinated Ni2+ (NiIV) by selectively removing microcrystalline NiOx using the impregnation-complexation strategy. The Niσ+ species derived from NiIV exhibited high propylene selectivity (∼88 %) and low coke yield (2.26 %) in PDH. In contrast, reducing microcrystalline NiOx to Ni0 resulted in high methane selectivity and high coke yield (14.90 %). Theoretical calculations and experimental results indicate that this difference is attributed to the faster propylene desorption from Niσ+ as compared to that from Ni0. Therefore, catalysts with well-confined Niσ+ are selective in PDH. This study offers a rational strategy for designing Ni-based PDH catalysts.

Preparation of Sustainable Ni/SiO2 Catalysts from Rice Husk by Different Methods for CO2 Methanation.

Silicon dioxide (SiO2) from rice husk can be extracted and be used as support for Ni-based catalysts. The impregnation method (IM) is usually used for preparing Ni/SiO2 catalysts, but its catalytic activity in CO2 hydrogenation to CH4 remains unsatisfactory. In this work, we explored alternative preparation methods, using ammonia evaporation method (AEM) and hydrothermal method (HM) to prepare the catalysts. The results showed that the catalysts prepared by AEM and HM were significantly superior to that prepared by IM. Notably, the catalyst synthesized by AEM from sustainable silica exhibited the best performance, achieving 81.69% CO2 conversion and over 99% methane selectivity at low reaction temperature of 300 °C. The characterization techniques indicate that the Ni/SiO2-AEM catalyst can form nickel phyllosilicate with lamellar structure, leading to better Ni dispersion and higher specific surface area. Furthermore, the results of in-situ DRIFTS have revealed the potential catalytic mechanism over Ni/SiO2 catalysts, indicating that it involves pathways with both the CO* and HCOO* as the key intermediates.

Size-dependent activity modulation of supported Ni nanocatalysts for efficient solid-state hydrogen storage in magnesium

The activity of Nickel (Ni)-based catalysts strongly depends on their particle size and dispersion; however, achieving controllable preparation of uniform particle size with high activity remains a great challenge for Ni-based catalysts to promote efficient hydrogen storage. Here, we employ a facile Carbothermal Shock (CTS) method to obtain carbon fiber-loaded Ni-based nanocatalysts (Ni@CC) with high dispersibility and size-dependent properties, which can exhibit superior catalytic effects for solid-state hydrogen storage in MgH2. It was found that the shorter the CTS duration, the smaller the size of the Ni nanoparticles, and the better the catalytic effect. Among these, the MgH2-Ni@CC with a CTS duration of 30 s showed the best hydrogen storage performance. Its activation energy for hydrogen release was significantly decreased from 158.3 kJ⋅mol−1 for milled MgH2 to 98.6 kJ⋅mol−1. More importantly, the retention rate of hydrogen absorption capacity is 95.1 % after 30 cycles, which far exceeds the 65.5 % retention rate observed in milled MgH2. These property enhancements can be attributed to the presence of nano-sized Ni and its in situ derived Mg2Ni intermediate phases, which create more channels for hydrogen atoms diffusion. Meanwhile, the close contact between nano-Ni and the Mg/MgH2 matrix can provide active catalytic sites and low-energy interfaces for facilitating hydrogen adsorption and desorption. Our study presents a promising approach to significantly improve the hydrogen storage performance of MgH2 by modulating size-dependent catalytic activity.

Simple construction of efficient graphite supported NiCoCu functional catalysts for methanol oxidation reaction using mechanical milling

A low-energy methodology has been proposed to synthesized Ni-based binary and ternary compounds from M-acetylacetonates (M = Ni, Co and Cu) and mechanical milling (MM) to be used as electrocatalysts for the methanol oxidation reaction in alkaline medium (1 M KOH). The strategies used in this study expand the possibilities of obtaining materials with efficient electrocatalytic activities from noble metal-free catalysts, while reducing the production cost. The prepared electrodes were characterized to evaluate changes in the thermal decomposition, as well as chemical, structural, morphological and microstructural changes with the composition. Electrochemical performance was evaluated by conventional methods such as cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The series of Ni-based catalysts demonstrated that after MM the composites integrate with oxides of the individual metallic materials without the formation of solid solutions. The electrocatalytic mass activities of the as-obtained composites were found in the following order: Ni0.80Co0.10Cu0.10/C (1181.14 A/g) ≅ Ni0.8Cu0.2/C (1124.45 A/g) > Ni0.80Co0.05Cu0.15/C (254.50 A/g) > Ni0.80Co0.15Cu0.05/C (209.34 A/g) > Ni0.8Co0.2/C (136.64 A/g). Among them, Ni0.80Co0.10Cu0.10/C showed the greatest stability and the leastwest charge transfer resistance that ranges between 0.28 and 0.80 Ω depending on the methanol concentration, and also presented activities higher than those of the commercial Pt/C catalysts. The results demonstrate that with this simple method, it is possible to modulate the electronic structure reducing CO poisoning on the surface of the catalysts and act as an alternative to replace high-cost noble metals during energy conversion from methanol.

Improvement of methane reforming Ni-based catalyst stability by controlling the unsaturated coordination aluminum in metakaolinite

Dry reformation of methane (DRM) is an attractive route to utilize greenhouse gases, which has significant environmental and economic benefits. Ni-based catalysts are one of the most important catalysts in DRM. However, their deactivation induced by sintering and coking remains a major challenge. In this work, a series of metakaolinite-supported Ni catalysts (Ni/MK) with varying content of unsaturated coordinated aluminum were prepared. It was found that the catalytic stability could be improved by controlling the unsaturated coordinated aluminum content. Ni/MK-800, with the highest unsaturated coordinated aluminum content, demonstrated at least 18 times enhanced stability duration compared with Ni/MK-600 with the lowest content. The increasing content of unsaturated coordinated aluminum enhanced the metal-support interaction, which subsequently improved the anti-sintering and anti-coking performance and thus improved the catalytic stability. This work provided an optional strategy for designing highly stable DRM catalysts by controlling the coordinative unsaturation degree of central ions in support.

Tailoring the Hydrogen Spillover Effect in Ni-Based Heterostructure Catalysts for Boosting the Alkaline Hydrogen Oxidation Reaction.

Improving the catalytic efficiency of platinum group metal-free (PGM-free) catalysts for the sluggish alkaline hydrogen oxidation reaction (HOR) is crucial to the anion exchange membrane fuel cell. Recently, numerous Ni-based heterostructures have been designed based on bifunctional theory to enhance HOR activity by optimizing the binding energy of both H* and OH*; however, their activities are still far inferior to those of PGM catalysts. Indeed, the long transfer pathway for intermediates between different active sites in such heterostructures has rarely been investigated, which could be the reason for the bottleneck. Here, we design a Ni/MoOxHy heterostructure catalyst to promote H* migration from the Ni side to the interface for alkaline HOR via the hydrogen spillover effect. In situ X-ray absorption fine structure, Raman characterizations, H/D kinetic isotope effects, and theoretical calculations have proven facile H* migration from the Ni side to the interface, which further reacts with OH* on the MoOxHy surface. Besides, the hydrogen spillover effect is also beneficial for the preservation of the metallic phase of Ni during the reaction. The catalyst exhibits a high activity with Jk,m of 58.5 mA mgNi-1 and j0,s of 42 μA cmNi-2, which is among the best PGM-free catalysts and is even comparable to some PGM catalysts. It also shows the highest power density (511 mW cm-2) as a PGM-free anode when assembled into fuel cells under moderate back pressure. These findings prove that in addition to optimizing electrophilicity and oxophilicity for active sites, we could also improve the HOR activity from the transfer pathway for intermediates, which provides insight into the design of other efficient HOR catalysts.

Ba2+ doping into Ni/Al2O3 nanofibers promotes CO2 methanation via alkaline modulation

Ni-based catalysts are promising catalysts for CO2 methanation due to low lost. However, the activity and selectivity of Ni-based catalysts in CO2 methanation at low temperatures still need to be improved. Here, Ni4Al2BamOx (m = 0–0.5) nanofibers were prepared. Doping Ba2+ would increase alkaline sites and facilitate generating oxygen vacancies. Especially, Ni4Al2Ba0.2Ox exhibited the high specific surface area with 127.1 m2 g−1, being potential for exposing more active sites. Indeed, compared with undoped Ni4Al2Ox catalysts (CO2 conv. = 45 %, CH4 select. = 92 % at 300 °C), Ba2+ doping significantly improved activity (CO2 conv. = 74 %, CH4 select. = 99 % at 300 °C) and stability within 200 h for Ni4Al2Ba0.2Ox. Both EPR and O1S XPS confirmed that Ni4Al2Ba0.2Ox can form more oxygen vacancies and CO2-TPD confirmed that Ni4Al2Ba0.2Ox had stronger CO2 adsorption capacity compared to Ni4Al2Ox. In-situ infrared spectroscopy and DFT calculations both indicated that Ba2+ doping can promote generating surface hydroxyl groups and formate pathways.

Unlocking Fe(III) Ions Improving Oxygen Evolution Reaction Activity and Dynamic Stability of Anodized Nickel Foam.

Fe has been reported to play a crucial role in improving the catalytic activity and stability of Ni/Co-based electrocatalysts for the oxygen evolution reaction (OER), while the Fe effect remains intangible. Here, we design several experiments to identify the activity and stability improvement using porous anodized nickel foam (ANF) as the electrode and 1.0 M KOH containing 1000 μM Fe(III) ions as the electrolyte. Systematic investigations reveal that Ni sites serve as hosts to capture Fe ions to create active FeNi-based intermediates on the surface of ANF to improve the OER activity significantly, and Fe ions regulate catalytic equilibrium and maintain the stability for a long time. The system exhibits 242 and 343 mV overpotentials to reach 10 and 1000 mA cm-2 current densities and a robust stability of 360 h at an industrially suitable current density (1000 mA cm-2). This work expands insights into the Fe(III) catalysis effect on the OER efficiency of Ni-based catalysts and provides an economical and practical way to commercial application.

The promotion mechanisms of Mo for the dry reforming of methane reaction over a Mo-doped Ni(2 1 1) bimetallic catalyst

With the escalating severity of climate change, the DRM reaction has gained attention as an effective pathway for utilizing CO2. Enhancing reaction activity and identifying the sources of carbon deposition during the DRM reaction on Ni-based catalysts pose crucial yet challenging questions. In this study, we investigate the effects of Mo doping on the reaction activity and carbon deposition of Ni catalysts using a combined DFT and microkinetic method. In terms of the models, Mo replaced one Ni atom in the surface and subsurface layers to represent Mo in the initial stages and in prolonged on the reaction, namely NiMoU(211) and NiMoL(211). Through the analysis of electronic structure, intermediate structures, and reaction barriers compared with Ni(211), the impact of Mo doping on the surface activity and carbon deposition of Ni(211) is studied. The results indicate that the strong Ni-Mo interaction enhances intermediate stability, leading to increased reaction activity. Mo doping promotes the increase in O concentration, but at low temperatures, reaction rates decrease sharply. Furthermore, Mo doping enhances the resistance to carbon deposition on Ni(211) surfaces and improves the ability to remove carbon deposits, especially in prolonged reaction models. These findings provide new mechanistic insights into the DRM reaction on Ni(211) surfaces, which were previously well-explained by experimental results, and are valuable for understanding quantum processes.

Catalytic hydrodeoxygenation of lignin-derived phenolic compounds with Ni-based aluminum phosphate catalyst

Lignin-derived products possess high carbon content and offer significant potential to be used as liquid fuels. However, they also contain high oxygen element and unstable functional groups. Hydrodeoxygenation (HDO) is an effective method for upgrading lignin-derived phenolic compounds to produce high-quality liquid biofuels. In this study, a series of Ni-based phosphate catalysts incorporating various metals (Al, Ce, La) were prepared and employed for the HDO of lignin-derived phenolic compounds. The results showed that Ni/AlPO4 had the most efficient HDO performance, with guaiacol conversion of 99.9 % and cyclohexane selectivity of 91.1 % at the reaction temperature of 250 °C. Various catalyst characterization measurements were conducted to assess the impact of metal phosphate species on the crystallography, morphology, physicochemical characteristics and surface properties. Results indicated that Ni/AlPO4 catalyst exhibited stronger acidity, smaller Ni particle sizes and larger specific surface area than other Ni-based phosphate catalysts. Based on the characterization results and experimental data, the corresponding HDO reaction pathways and mechanisms were also proposed. Ni/AlPO4 catalyst was also applied to the HDO of various lignin-derived phenol compounds and achieved a good HDO effect. Moreover, the catalytic upgrading of lignin-oil was also carried out, and a high proportion of hydrocarbon products that increased from 16.0 % to 88.6 % was obtained. This Ni/AlPO4 catalyst provides potential reference for the HDO application of lignin-derived phenolic compounds for the production of hydrocarbon liquid fuels.

High coke resistance Ni-based CH4/CO2 reforming catalysts with strong spatial confinement effect: Effect of CeO2 shell thickness

Ni-based catalysts show promise as candidates for the dry reforming of methane (DRM), yet the susceptibility to sintering and carbon deposition is a major obstacle to industrialization. This work demonstrates a mesoporous Ni-based catalyst with a thickness-tailorable CeO2 shell for enhanced spatial confinement effect for the DRM. The Ni-MCM-41@xCeO2 catalysts are prepared at various CeO2 shell thickness through a two-step hydrothermal reaction. The kinetic studies have shown that the Ni-MCM-41@2CeO2 catalyst has the lowest activation energy, producing a high conversion of CH4 and CO2 as high as around 80 % at 700 °C. Our characterizations reveal that the Ni core is tightly confined in the mesoporous skeleton of MCM-41 and within a CeO2 shell. The Ni-MCM-41@2CeO2 catalyst is able to sustain high activity for more than 10 h of operation, with a remarkably reduced carbon deposition (0.28 %) as compared with a conventional Ni-Ce/MCM-41 catalyst (8.77 %). Furthermore, the density functional theory (DFT) calculation supports that the CeO2 shell layer significantly reduces dissociation potential barrier for CH4 and CO2, hence enhancing the catalytic activity of the DRM.

Enhancing low-temperature CO2 methanation performance by selectively covering Ni with CeO2 to form Ni-O-Ce interface active sites

The methanation of CO2 is crucial for resource utilization, however, achieving excellent CO2 methanation performance with Ni-based catalysts at low temperatures remains highly challenging. In this study, a high-performance 10Ni-0.1Ce/Al catalyst was synthesized using a simple and efficient one-pot combustion method. Unlike other catalysts with the same components, this catalyst exhibits a unique feature where a small amount of the CeO2 promoter is dispersed on the support, while the majority selectively binds to and coats the Ni nanoparticles. This distinctive structure allows it to achieve approximately 80 % CO2 conversion and 99.9 % CH4 selectivity under conditions of 260 °C, 0.1 MPa, and a GHSV of 48,000 mL·g−1·h−1. The high catalytic performance is attributed to the unique structure of Ni nanoparticles and CeO2, which promotes the formation of numerous Ni-O-Ce interface active sites. These Ni-O-Ce interfaces enhance the reducibility and increase the content of weak basic sites in the catalyst. The combination of in-situ DRIFTS and TPSR reveals that the decomposition of bridged HCOO– to *CO is the rate-determining step. The presence of Ni-O-Ce interface active sites in the 10Ni-0.1Ce/Al catalyst facilitates the generation of abundant bridged HCOO– intermediates with higher activity than the 10Ni/Al catalyst, leading to a substantial enhancement in catalytic performance.

Applications of Ni-Based Catalysts in Photothermal CO2 Hydrogenation Reaction.

Heterogeneous CO2 hydrogenation catalytic reactions, as the strategies for CO2 emission reduction and green carbon resource recycling, play important roles in alleviating global warming and energy shortages. Among these strategies, photothermal CO2 hydrogenation technology has become one of the hot catalytic technologies by virtue of the synergistic advantages of thermal catalysis and photocatalysis. And it has attracted more and more researchers' attentions. Various kinds of effective photothermal catalysts have been gradually discovered, and nickel-based catalysts have been widely studied for their advantages of low cost, high catalytic activity, abundant reserves and thermal stability. In this review, the applications of nickel-based catalysts in photothermal CO2 hydrogenation are summarized. Finally, through a good understanding of the above applications, future modification strategies and design directions of nickel-based catalysts for improving their photothermal CO2 hydrogenation activities are proposed.

Impact of nickel and alkaline earth metals interaction on sustainable carbon nanotubes generation from plastic face masks via catalytic pyrolysis

The one-pot synthesis of carbon nanotubes (CNTs) emerges as a promising approach for plastic valorization, owing to its simplicity and scalability. However, limited attention has been given to catalyst design for this method, particularly regarding the influence of Group 2 alkaline earth metal elements (X) on the Ni-based catalyst activity. This study investigates the impact of X on the catalytic activity of Ni towards sustainable CNTs synthesis using plastic face masks. The findings revealed that X influenced the carbon yield of NiMo-X catalysts and the morphology of the resultant carbon nanomaterials. Notably, NiMo-Ca demonstrated the highest carbon yield, whereas NiMo-Mg and NiMo-Ba exhibited the lowest. Furthermore, NiMo-Mg tends to produce clean and thin CNTs, while NiMo-Ba tends to yield carbon flakes with numerous irregular cokes. In addition to the effect of Ni crystallite size, which influences the transition from tubular to flake-like carbon structures, environmental factors are also considered. Specifically, NiMo-Mg generated a high CO2/CH4 environment, while NiMo-Ba exhibited slower catalytic cracking of polymeric chains from face masks, both of which were unfavorable for CNTs growth. Conversely, NiMo-Ca facilitated higher carbon recovery, likely due to its creation of a low CO2/CH4 environment via CO2 methanation. Optimization studies indicated that increasing pyrolysis temperatures and durations lead to reduced carbon yield, while cyclic pyrolysis of face masks up to five iterations enhances the reusability of NiMo-X catalysts with improved carbon recovery. Overall, this study provides valuable insights into the early pyrolytic gas formation and carbon nucleation phase, which are influenced by the surface Ni fraction and Ni polarization, as well as the later CNTs growth phase, which is related to the Ni crystallite size.

Ni-Sr/TiZr for H2 from methane via POM: Sr loading & optimization.

Achieving remarkable H2 yield with significantly high H2/CO over Ni-based catalysts through partial oxidation of methane (POM) is a realistic approach to depleting the concentration of CH4 and using H2 and CO as synthetic feedstock. This study examined Ni catalysts on titania-zirconia for methane conversion via POM at 600 °C and atmospheric pressure. The addition of strontium to the catalyst was explored to improve its performance. Catalysts were characterized by X-ray diffraction, Raman-infrared-UV-vis spectroscopy, and Temperature-programmed reduction-desorption techniques (TPR, TPD). 2.5 wt% Sr addition induced the formation of the highest concentration of extreme basic sites. Interestingly, over the unpromoted catalyst, active sites are majorly generated by hardly reducible NiO species whereas upon 2.5 wt% promoted Sr promotional addition, most of active sites are derived by easily reducible NiO species. 45% CH4 conversion and 47% H2 yield with H2/CO = 3.5 were achieved over 2.5 wt% Sr promoted 5Ni/30TiO2 + ZrO2 catalyst. These results provide insight into the role of basic sites in enhancing activity through switching indirect pathways over direct pathways for POM. Further process optimization was carried out in the range of 10 000-22 000 SV, 0.35-0.75 O2/CH4, and 600-800 °C reaction temperature over 5Ni2.5Sr/30TiO2 + ZrO2 by using central composite design under response surface methodology. The optimum activity as high as ∼88% CH4 conversion, 86-87% yield of H2, and 2.92H2/CO were predicted and experimentally validated at 800 °C reaction temperature, 0.35O2/CH4 ratio, and 10 000 space velocity.

Highly dispersed Ni nanoparticles confined in mesoporous SBA-15 for methane dry reforming with improved coke resistance and stability

Methane dry reforming (DRM) is a promising route for sustainable syngas production, in which Ni-based catalysts face challenges of metal sintering and coke formation. In this work, highly dispersed Ni nanoparticles (NPs) embedded in the mesopores of SBA-15 were prepared using a simple solid-state impregnation (SSI) method. TEM and cross-section HRTEM results clearly indicated that ultra-small Ni NPs (3–4 nm) were orderly dispersed within the mesopores of the SBA-15 support. Compared with the conventional wetness impregnation (WI) method, the Ni/SBA-15 catalyst prepared by solid-state impregnation method possessed much better catalytic activity, stability, and coke resistance in DRM. In-situ DRIFTS and semi-in-situ XRD were used to elucidate the dispersion and encapsulation mechanism of Ni within the mesopores of SBA-15 during the sample preparation process. Specifically, WI formed large NiO particles, while SSI formed smaller NiO NPs with stronger interaction between metal and support (SIMS) via forming Ni-O-Si species which is beneficial for the DRM reactivity. This work establishes relationships among catalyst preparation, structure, and DRM performance, paving the way for general template-assisted methods to prepare nanometallic catalysts for various applications.

Pollutant degradation and hydrogen production of landfill leachate membrane concentrates via aqueous phase reforming

Membrane filtration is a mainstream method for landfill leachate treatment, leaving the landfill leachate membrane concentrates (LLMCs) a high-toxicity residue. Conventional LLMCs disposal technology shows specific challenges due to the low biodegradability, high inorganic salts, and high heavy metal ions content of LLMCs. Therefore, it is necessary to degrade LLMCs with a more suitable technology. In this study, a special method was proposed to convert some organic chemicals into valuable compounds by aqueous phase reforming (APR). Ni-based catalysts (Ni//La2O3, Ni/CeO2, Ni/MgO, and Ni/Al2O3) were prepared to investigate the effect of different supports on the APR of LLMCs. APR performed outstanding characteristics in the decrease of chemical oxygen demand (COD) and total organic carbon (TOC), the degradation of macromolecules, and the removal of heavy metal ions in the aqueous phase. In addition, H2 was generated which is beneficial for energy compensating during the APR process. The best-performing catalyst (Ni/Al2O3) was selected to investigate the effects of reaction temperature, reaction time, and catalyst addition on product distribution. The optimal H2 selectivity (44.71%) and H2 production (11.63 mmol/g COD) were obtained at 250 °C with 2 g Ni/Al2O3 usage for 1 h. This paper provided a new perspective on the disposal of LLMCs, which will degrade pollutants efficiently.

Elucidating Pathways of Methanol Oxidation on Oxygen-Vacant NiOOH Sites Using a Synergistic in Situ Attenuated Total Reflectance Surface-Enhanced Infrared Absorption Spectroscopy and DFT Study

A thorough comprehension of the mechanism underlying the methanol oxidation reaction (MOR) on Ni-based catalysts is critical for electrocatalysis design and development of Ni-based alloys. However, the mechanism of MOR on these materials remains a matter of controversy. There have been few publications on employing surface enhanced spectroscopy to adequately capture the surface chemistry of MOR on NiOOH while the existing theoretical chemistry studies on the reaction mechanism presents a multitude of inconsistent and incomplete results. Here, we combine in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) to determine the mechanism and product distribution of MOR on monometallic Ni-based catalysts in alkaline media. Critically, the DFT calculations include the role of O-vacancy of NiOOH, which is argued to be the active site for methanol oxidation. The SEIRAS results show that two bands corresponding to nas(O=C–O) of HCOO- and nas(C–O) of HCO3 -/CO3 2- appears after the commencement of MOR and varies as a function of potentials. These spectroscopic results are in good agreement with the DFT-based energetics of reaction, suggesting that the MOR mainly proceeds in the following pathway: The early consumption of methanol yields HCOO- as the major product while increasing potentials stimulate further oxidation of adsorbed HCOO* to form HCO3 -/CO3 2-. On the other hand, we show a parallel pathway for the generation of HCO3 -/CO3 2- at high potentials that bypasses the formation of HCOO*. The two main pathways presented in this study are thermodynamically more feasible than the one predominantly reported in literature for MOR on NiOOH. The two former pathways circumvent CHO and/or CO to produce HCO3 -/CO3 2-, whereas the latter involves these species as intermediates. These DFT-based hypotheses are backed up by the spectroscopic evidence that no band associated with CHO and CO can be detected by SEIRAS. This study has the potential to offer invaluable atomic-level insights into MOR on NiOOH as a stepping stone to development of high-performance multi-metallic Ni-based catalysts. Figure 1

Exploring the Role of Coordinating Environments on Durability of Nickel-Based Catalysts for Hydrogen Evolution Reactions

Ni-based platinum-group-metal (PGM)-free catalysts for hydrogen evolution reaction have been considered viable for the commercialization of alkaline exchange membrane water electrolysis (AEMWE) due to their high activity and low cost. Even though several highly active Ni-based catalysts have been developed in recent years, their long-term stability under commercially relevant conditions was not systematically assessed, preventing a direct comparison with the currently used catalysts. While not as active, the current commercial PGM-free catalysts are highly stable, with an operational life measured in decades. However, conducting durability assessments through long-term durability studies can take over 10,000 hours which is impractical. Consequently, accelerated stress tests (ASTs) specifically targeting the catalyst and simulating uncontrolled shutdown and high overpotential scenarios are needed to further improve AEMWE technology.In this presentation, the ASTs of several Ni-based catalysts with different coordination environments (nickel molybdenum, nickel cupferron1, Ni-NiO, and a novel high surface area de-alloyed Ni catalyst) will be explored. The catalysts were subjected to high overpotentials and uncontrolled shutdown cycles in both liquid electrolyte and AEMWE cells. The structure of these catalysts was observed using in situ Raman spectroscopy, XRD, TEM, and BET gas adsorption analysis and correlated to changes in electrochemical performance. The determination of the catalyst structure during these ASTs is paramount in designing durable PGM-free catalysts for improved AEMWE performance.1) Doan, H.; Kendrick, I.; Blanchard, R.; Jia, Q.; Knecht, E.; Freeman, A.; Jankins, T.; Bates, M. K.; Mukerjee, S. Functionalized Embedded Monometallic Nickel Catalysts for Enhanced Hydrogen Evolution: Performance and Stability. J. Electrochem. Soc. 2021, 168 (8), 084501. https://doi.org/10.1149/1945-7111/ac11a1.

Syntheses of Ni-Based Layered-Double Hydroxide Materials Via Liquid Phase Deposition Method for Alkaline Water Electrolysis

For the sustainable society, hydrogen production has received much attention during decades. The alkaline water electrolysis process has been recognized as one of the important processes for hydrogen products. For the achievements of an effective water electrolysis system, the decrease of the overpotential on the oxygen evolution reaction (OER), which is the four-electron and proton transfer process. These complex 4-electron sluggish processes lead to the large energy losses in the whole water electrolysis. Although the noble catalysts such as IrO2 or RuO2 exhibit high OER activity, their large-scale applications are limited due to cost problem. From this point of view, the low-cost transition metal materials, especially Ni-based catalysts, have been extensively studied. And also, it has been reported that the well-defined layered double hydroxide (LDH) structures can promote water oxidation through the interlayer anion effects. Despite this fact, the specific procedures for the preparation of Ni-based LDH structures have not been well established. Therefore, in this study, we have investigated the preparation of Ni-based LDH structures in the aqueous solution at room temperature, the so-called liquid phased deposition (LPD) method.Through the LPD method, we have synthesized various types of Ni-based LDH structures. As an example, the Ni-Al LDH structures were synthesized on the conductive substrate. It was found that our synthesized Ni-Al LDH exhibited relatively high OER activity and durability against electrochemical potential cycling [1]. In addition, the dependencies of the OER activity on the interlayer anion species were clearly demonstrated. In addition, the other types of Ni alloy LDHs were also prepared and their OER activity was investigated. Through the electrochemical measurements, we have confirmed the advantages of our materials prepared by LPD methods as an anode for alkaline water electrolysis.