Non-precious Catalysts Research Articles

Probing Mixed Phase Metallic Ni/Amorphous Nickel Phosphide Nanocatalysts during Oxygen Evolution Reaction Using Operando X-Ray Absorption Spectroscopy

Metal phosphide-containing nanomaterials have demonstrated remarkable efficacy as non-precious metal-based catalysts for the alkaline oxygen evolution reaction (OER). While it is widely acknowledged that various OER catalysts undergo structural reconstruction under applied OER potentials, monitoring these changes is challenging because they are often rapid and require instrumentation not typically found in the typical lab setting. In this study, we utilize operando X-ray absorption spectroscopy (XAS) to determine the structural reconstruction of nickel-based metal phosphide catalysts during OER. We have developed the synthesis of nickel-based phosphide nanoparticles with a range of phosphorus incorporation. These nanoparticles are composed of metallic nickel and amorphous nickel phosphide phases as determined by XRD, TEM and XAS. At low levels of P incorporation, from 2% to 15%, the synthesis results in the mixture of metallic nickel and amorphous phosphide phases. At higher levels of phosphorus incorporation, from 20% to 30%, amorphous nickel phosphide is the predominant phase. Electrochemical characterization of this nickel phosphide series for OER revealed that the catalysts with 20% phosphorus incorporation exhibited superior OER activity. The phosphides with lower phosphorus content, such as 2%, had smaller Ni2+/Ni3+ redox peaks which has been shown to suppress the conversion to Ni(OH)2, leading to lowered OER activity. Increased amorphous nickel phosphide phase led to greater activity, suggesting that the active component in the catalyst comes from the amorphous nickel phosphide phase. Meanwhile, higher phosphorus content (20-30%) where the amorphous phosphide is the predominate phase resulted in larger redox peaks, signifying greater conversion to Ni(OH)2. Operando XAS will be applied to investigate these metallic nickel/nickel phosphide nanocatalysts to elucidate their structural reconstruction during OER

Toward Sustainable Olefins: Electroreduction of CO2 to Multi-Carbon Olefins Using Trimetallic Cu-Rich Catalysts

The sustainable conversion of carbon monoxide (CO2) into value-added chemicals via electrochemical methods, powered by renewable electricity, is considered as a promising approach to meet the global energy demand and close the anthropogenic carbon cycle. However, this technology is in the early stage of development, particularly in the production of multi-carbon (C2+) hydrocarbons due to well-studied thermodynamic and kinetic barriers. To overcome these challenges, developing a catalyst with high activity and selectivity is crucial to minimize energy input and maximize the effectiveness of C2+ products formation.In this work, we will present our recent advancement on developing non-precious tri-metallic catalysts with copper-rich surface synthesized by our developed atomically controllable and environmentally friendly synthesis method. The developed nanostructured tri-metallic electrocatalysts by this method show remarkable selectivity and activity in the electrochemical conversion of CO2 to olefins. In particular, our electrochemical results show an overall C2+ olefine Faradaic efficiency (FE%) of 69% more specifically 58% ethylene and 11% propylene at a current density of -112 mA/cm² under applied potential of -2.8 V in an anion exchange membrane (AEM) electrolyzer. To gain a better understanding of the catalytic performance and find a structural-performance relationships for the developed materials, we performed several physicochemical and electrochemical characterization experiments, including X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and X-ray photoelectron spectroscopy (XPS). We will discuss morphology and atomic structure changes of the developed materials under realistic conditions, with a specific focus on understanding how different trimetallic interfaces influence selectivity and activity in the electrochemical CO2 reduction reaction (eCO2RR).

Understanding the Degradation Mechanism for NiMo Composite and Effect of Ionomer on the Activity Towards HER

Hydrogen is an essential commodity for achieving cleaner and greener energy.1,2 Due to its high gravimetric energy density, hydrogen is favored as a carbon-neutral fuel.2,3 Moreover, the electrochemical accessibility of hydrogen evolution and oxidation reactions enable hydrogen to be used as a reversible fuel, as in hydrogen battery anodes and unitized reversible fuel cells.4,5 Platinum group metals (PGMs) are excellent catalyst for hydrogen chemistry, as they exhibit negligible activation barrier for HER and HOR, but they are costly and the upstream processes for mining and purification are unsustainable.6 A promising alternative to PGM catalysts would be nonprecious transition metal alloys/composites in form of nanoparticles. These materials are more readily available and lower in cost. Nonetheless, non-precious catalysts developed to date have never met the benchmarks set by PGMs in terms of catalytic activity and stability.Our lab is continuing a long-running effort to develop and improve nickel-molybdenum (Ni–Mo) composites, which stand as one of the strongest candidates for non-PGM HER and the HOR. In prior work, we developed a method to synthesize Ni–Mo nanoparticles supported on oxidized carbon, which increases catalyst dispersion and significantly reduces losses due to interfacial resistivity.7 The catalyst composite has a core@shell structure, where in the core is mainly nickel-rich alloy and the shell is primarily molybdenum-rich oxide.Furthermore, DFT calculations suggest the addition of Mo in the catalyst subsurface weakens hydrogen binding to surface Ni sites, thus increasing the overall activity toward HER/HOR.8 In ongoing work to further develop Ni–Mo/C composites, we are focusing on catalyst degradation under storage and operating conditions. To examine catalyst durability upon extended storage, we measured activity toward hydrogen evolution progressively for a single batch of catalyst powdered retained at room temperature in an aerobic environment over 850 hours. We observed a monotonic decrease in catalytic activity culminating in a >90% decrease in activity. Post-mortem analysis via XRD showed the increased peak intensities corresponding to NiO and MoO3. We further observed that the catalyst remains active over extended periods when stored under a dry, oxygen-free atmosphere. Finally, exposing the degraded catalyst to thermal reduction increased catalytic activity. Together, these results strongly suggest aerobic oxidation as the primary degradation mechanism under shelf-storage, with straightforward mitigations steps readily available by excluding air and water. This finding further suggests that oxide component of the synthesized catalyst is not an active site for hydrogen chemistry, although we speculate that some surface oxide is beneficial for enhancing the rate of water dissociation.9 We also studied the impact of the ionomer chemistry on the catalytic activity of Ni–Mo composites for alkaline anion exchange membrane (AEM) electrolyzer applications. Surprisingly, we observed an ~80% reduction in catalytic activity for Ni–Mo composites formulated into thin film HER catalysts using poly(aryl piperidinium) (PAP) carbonate AEM ionomers relative to control samples based on Na-exchanged Nafion ionomer binders. Further work showed this result was specific to the carbonate form of the ionomer, as HER activity was fully recovered when we used halide forms of the PAP ionomer. Work is ongoing to establish the physicochemical basis of this poisoning effect.Based on these findings, we developed functional AEM electrolyzer assemblies with IrOx anodes and Ni–Mo/C cathodes, where the cathode composition was formulated based on our best results from RDE studies. These MEAs yielded electrolyzer performance properties that were indistinguishable from MEAs we tested using Pt–Ru/C cathodes that were otherwise identical in composition.8 This leads us to conclude that advanced Ni–Mo/C catalyst composites can indeed achieve performance parity with PGM catalysts on the basis of initial catalytic activity, whereas significant work remains to characterize durability under extended operating conditions.

Amorphous W-doped iron phosphide with superhydrophilic surface to boost water-splitting under large current density

Electrochemical water-splitting is an effective approach for producing hydrogen without producing any pollutants, but its large-scale development is hampered by the lack of low-cost and efficient electrocatalysts. Therefore, it is essential to explore efficient and low-cost non-precious catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, W-doped Fe-P/IF amorphous nanoflake arrays (W-Fe-P/IF) are synthesized by corrosive avenue and following low-temperature phosphorization. Benefiting from the superhydrophilic surface, amorphous structure, nanosheet morphology and abundant active sites, the synthesized catalysts exhibited good catalytic performance. Therefore, the W-Fe-P/IF electrocatalyst onws low overpotentials of 35, 67, and 105 mV to achieve 10 mA cm−2 in 1 M KOH, 1 M KOH + seawater, and 1 M PBS, respectively. In addition, it also exhibits low voltage of 1.63 V to obtain 10 mA cm−2 coupled with excellent stability under 500 mA cm−2. The work provides a new strategy for the preparation of highly-efficient and low-cost non-precious electrocatalysts on renewable energy-related applications.

One-Pot construction of highly active hetero-interface over porous non-stoichiometric perovskite with gel combustion strategy to enhance toluene purification activity

Constructing active perovskite nanostructures by a simple method is of great value and significance to the practical application of non-precious metal oxide-based catalysts. Herein, a surfactant-assisted gel combustion approach was adopted to fabricate a state-of-the-art LaMnO3 perovskite catalyst with a rich porous structure and hetero-interface, which can be active for low-temperature purification of toluene. Due to the large amount of gas produced during the decomposition of surfactant, the obtained catalysts own a rich porous structure, which results in a higher specific surface area and exposes more active sites. Significantly, the highly active Mn2O3-LaMnO3 hetero-interface can be generated over the non-stoichiometric perovskite successfully through adjusting the proportion of B-site element. The introduction of hetero-interfaces alters the surface structure of the material with more oxygen vacancies, leading to a significant promoting effect. It is found that the T90 of toluene (1000 ppm in air) conversion over the sample with 30 % excess manganese (La: Mn = 1: 1.3) is only 289 °C at a relatively high weight hourly space velocity (WHSV = 120,000 mL•g−1•h−1), which is 87 °C lower than that of stoichiometric LaMnO3 perovskite. This work presents a versatile strategy for preparing highly active non-precious metal catalysts for industrial applications.

Revealing Structural Evolution of Nickel Phosphide-Iron Oxide Core-Shell Nanocatalysts in Alkaline Medium for the Oxygen Evolution Reaction.

Metal phosphide-containing materials have emerged as a potential candidate of nonprecious metal-based catalysts for alkaline oxygen evolution reaction (OER). While it is known that metal phosphide undergoes structural evolution, considerable debate persists regarding the effects of dynamics on the surface activation and morphological stability of the catalysts. In this study, we synthesize NiP x -FeO x core-shell nanocatalysts with an amorphous NiP x core designed for enhanced OER activity. Using ex situ X-ray absorption spectroscopy, we elucidate the local structural changes as a function of the cyclic voltammetry cycles. Our studies suggest that the presence of corner-sharing octahedra in the FeO x shell improves structural rigidity through interlayer cross-linking, thereby inhibiting the diffusion of OH-/H2O. Thus, the FeO x shell preserves the amorphous NiP x core from rapid oxidation to Ni3(PO4)2 and Ni(OH)2. On the other hand, the incorporation of Ni from the core into the FeO x shell facilitates absorption of hydroxide ions for OER. As a result, Ni/Fe(OH) x at the surface oxidizes to the active γ-(oxy)hydroxide phase under the applied potentials, promoting OER. This intriguing synergistic behavior holds significance as such a synthetic route involving the FeO x shell can be extended to other systems, enabling manipulation of surface adsorption and diffusion of hydroxide ions. These findings also demonstrate that nanomaterials with core-shell morphologies can be tuned to leverage the strength of each metallic component for improved electrochemical activities.

Dynamic stereomutation of vinylcyclopropanes with metalloradicals

The ever increasing demands for greater sustainability and lower energy usage in chemical processes call for fundamentally new approaches and reactivity principles. In this context, the pronounced prevalence of odd-oxidation states in less precious metals bears untapped potential for fundamentally distinct reactivity modes via metalloradical catalysis1–3. Contrary to the well-established reactivity paradigm that organic free radicals, upon addition to a vinylcyclopropane, lead to rapid ring opening under strain release—a transformation that serves widely as a mechanistic probe (radical clock)4 for the intermediacy of radicals5—we herein show that a metal-based radical, that is, a Ni(I) metalloradical, triggers reversible cis/trans isomerization instead of opening. The isomerization proceeds under chiral inversion and, depending on the substitution pattern, occurs at room temperature in less than 5 min, requiring solely the addition of the non-precious catalyst. Our combined computational and experimental mechanistic studies support metalloradical catalysis as origin of this profound reactivity, rationalize the observed stereoinversion and reveal key reactivity features of the process, including its reversibility. These insights enabled the iterative thermodynamic enrichment of enantiopure cis/trans mixtures towards a single diastereomer through multiple Ni(I) catalysis rounds and also extensions to divinylcyclopropanes, which constitute strategic motifs in natural product- and total syntheses6. While the trans-isomer usually requires heating at approximately 200 °C to trigger thermal isomerization under racemization to cis-divinylcyclopropane, which then undergoes facile Cope-type rearrangement, the analogous contra-thermodynamic process is herein shown to proceed under Ni(I) metalloradical catalysis under mild conditions without any loss of stereochemical integrity, enabling a mild and stereochemically pure access to seven-membered rings, fused ring systems and spirocycles.

First principles energetic span analysis of the activity of transition metal catalysts for N2O decomposition: The reversal of descriptor roles in the presence of NO

The utilization of NH3 combustion faces a significant hurdle in mitigating N2O emissions, a potent greenhouse gas. Current deNOx technologies struggle to effectively decompose N2O, especially under practical conditions due to inhibitory effects from exhaust stream components like O2, NOx, and H2O. This study employs first principles investigations to analyze N2O decomposition activity on precious (Ru, Rh), non-precious (Cu, Ni), and hybrid (Ru/Cu, Rh/Cu, Ru/Ni, Rh/Ni) catalysts. Many new Brønsted-Evans-Polanyi relations are established, enabling mechanistic analysis via the Energetic Span Model. The analyses reveal opportunities for enhancing catalytic activity by exploiting weak correlations between intermediates’ free energies. The model captures the inhibitory effects of surface-adsorbed NO on the N2O decomposition activity, aligning well with experimental observations and catalytic trends. The strong binding energy of adsorbed N2/N2O and O adatom is found to be a key descriptor of activity. It is found to aid the catalytic activity in the presence of NO but becomes limiting in its absence.

Crystal phase engineering of CoBOx/NiCoP heterostructures as trifunctional electrocatalysts for overall water splitting and urea electrolysis

Rational design of non-precious metal-based catalysts for value-added chemicals production is crucial but still challenging. Herein, a trifunctional electrocatalyst with heterostructures is developed via phosphating and NaBH4 pretreatment of the pristine ZIF-L for overall water splitting and urea oxidation. The as-prepared CoBOx/NiCoP catalyst exhibits superior electrocatalytic performance with only overpotentials of 100, 283 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) to reach the current density of 10 and 100 mA cm−2, respectively, and the low potential of 1.35 V to achieve a current density of 100 mA cm−2 for urea oxidation reaction (UOR). Theoretical calculations show that the construction of amorphous/crystalline heterostructure can accelerate the charge transfer between the active site and intermediate, thus enhance the intermediates adsorption and reduce the kinetic barrier toward HER/OER process for enhancing electrocatalytic activity. Importantly, the in-situ Raman spectroscopy discloses that the rapid formation of oxidation-state transition metal oxyhydroxide species would provide more active sites for the oxidation reaction. This multiple electrocatalysis demonstrates the great potential of amorphous/crystalline heterogeneous interfaces for high-performing electrocatalytic conversions.

Superior electrocatalytic nitrate-to-ammonia conversion activity on CuCo bimetals in neutral media

Electrocatalytic recycling of waste nitrate (NO3-) to valuable ammonia (NH3) has been regarded as a sustainable and promising alternative to the unfriendly Haber-Bosch process. Nevertheless, it is still a challenge to achieve high production rate in a neutral media due to the multi-step electron and proton transfer process. Herein, a nonprecious CuCo tandem catalyst is facilely fabricated and the cooperative active sites enable efficient cascade NO3--to-NH3 conversion with outstanding Faradaic efficiency (FE) and high-rate NH3 generation (95 %, 710 μmol h−1 cm−2 at −0.65 VRHE) in neutral media. In-situ Fourier transform infrared spectroscopy (FTIR) is implemented to identify the reaction intermediates to figure out the tandem pathway. Further combined the density functional theory (DFT) calculations, the structure-activity relationship is unveiled. The introduction of Cu regulates the electronic structure of Co to boost the adsorption capacity of nitrate and shifts the d-band to lower the energy barrier. Moreover, the presence of Cu plays a vital role in inhibiting the binding of H*, which ensures the superior FE. To further maximize the energy utilization efficiency, a two-electrode electrolyzer (Cu45Co55||CuNi) is assembled by replacing the anodic oxygen evolution reaction (OER) with thermodynamically favored 5-hydroxymethylfurfural (HMF) oxidation to produce value-added 2,5-furandicarboxylic (FDCA), an important intermediate in the synthesis of bioplastics. These findings might guide the rational design of efficient and inexpensive electrocatalysts to produce value-added chemicals and hold the promise for contributing to carbon peaking and neutrality goals.

Hydrogen production from Fraxinus mandshurica solid wood waste using FeCl3 as a non-precious metal Lewis acid catalyst: A comprehensive utilization approach

The efficient use of wood powder has become increasingly important for protecting the environment and addressing energy shortages. In this study, a proton exchange membrane electrolysis system was utilized to convert biomass into valuable industrial chemicals and hydrogen using ferric ions as redox mediators, reduced reaction costs. GC-MC analysis revealed that the degradation products are mainly consisted of aromatic carbonyl compounds, along with some alcohols, phenols, and alkanes. The degradation efficiency was found to be 55.6 %, and the Faraday’s hydrogen production efficiency exceeds 92.6 %. Moreover, Fe3+/Fe2+ redox mediators was recycled in the electrolysis system, maintaining high reactivity. This research introduces a new approach for the degradation of wood powder, offering potential for sustainable industrial production and a reduction in environmental impact.

Nitrogen-bridged Cu-Zn dual-atom cooperative interface sites for efficient oxygen reduction reaction in Zn-air battery

Developing nonprecious catalysts with excellent behaviors for oxygen reduction reaction (ORR) has assumed considerable importance, but remains an arduous issue. Herein, we demonstrate a Kirkendall effect-pyrolysis (KEP) strategy to construct N-bridged Cu-Zn dual-atom supported on hollow N-doped carbon (Cu-Zn DA/HNC) for ORR. The hollow structure of N-doped carbon facilitates mass transfer and exposes more actives. What’s more, the shared N atom between Cu and Zn atoms is beneficial to enhance their synergetic effect, creating an appropriately enhanced O* binding. The resulting Cu-Zn DA/HNC displays excellent ORR activity in an alkaline electrolyte, following a nearly four-electron pathway of ORR. Even employing Cu-Zn DA/HNC as the cathode in ZABs, Cu-Zn DA/HNC presents a long cycling life up to 910 h and robust low-temperature adaptability. The facile and straightforward fabrication plus the outstanding ORR performance of Cu-Zn DA/HNC endows its great potential as a significant candidate in practical applications of ZAB.

Enhanced hydrolysis of NaBH4 using cobalt sulphide for hydrogen production

The generation of pollution free hydrogen through NaBH4 hydrolysis using the suitable low cost catalysts is promising technique for sustainable green energy production. Herein, we report the facile synthesis of cobalt sulphide (CoS) using the hydrothermal technique and catalysed hydrolysis of NaBH4 for hydrogen generation. CoS nanoparticles show obvious catalytic performance with hydrogen generation rate (HGR) of 328 mL min−1 g−1cat at 25 °C in 2.9 % (1.5 g) NaBH4. Importantly, owing to low activation energy for hydrolysis of about 58.8 kJ mol−1 and efficient hydrolysis, CoS nanoparticles enables the NaBH4 hydrolysis with HGR of 319 mL min−1 g−1cat at 50 °C with 0.1 g NaBH4. The HGR is significantly enhanced from 119 mL min−1 g−1cat in dark to 214 mL min−1 g−1cat in illumination with 0.5 g NaBH4 and 60 mg catalysts. Finally, the present findings advocate the development of sulphide based non-precious catalysts for solar light driven hydrolysis of NaBH4.

Efficient hydrogen evolution activity of NiMoP electrodeposited on stainless steel mesh

In the context of industrial water electrolysis cells, the electrocatalyst often exhibits slow kinetics in water dissociation, allowing for reduced electrocatalytic performance in the production of hydrogen through water splitting. This report presents a novel ternary Nickel–Molybdenum–Phosphide (NiMoP) catalyst synthesis as a quick Tafel-step-decided electrocatalyst toward hydrogen evolution reaction (HER). Herein, we systematically evaluate the performance of various nickel-based catalysts when electrodeposited over the stainless-steel mesh (SSM) substrate for water electrolysis. The results reveal a diminishing trend in both the Tafel slope and overpotential in relation to the catalyst composition, following the order of Ni > NiMo > NiP > NiMoP. Consequently, NiMoP/SSM emerges as the top performer, displaying outstanding performance in terms of thermodynamics (the current density of 10 mA cm−2, η10 = 239 mV) and kinetics (STafel = 98.22 mV·dec⁻¹ at 1.0 M KOH) in water splitting. Thus, this novel ternary NiMoP catalyst with SSM, prepared through a straightforward and cost-effective synthesis method, holds great promise as a non-precious hydrogen evolution catalyst in water electrolyzing.

Non-precious Electrocatalysts for the Hydrogen Evolution Reaction

The development of non-precious metal-based catalysts for the hydrogen evolution reaction (HER) is a promising research area with the potential to advance water electrolysis and enable the widespread use of hydrogen as a clean energy source. While noble metals like Pt and Pd exhibit excellent HER activity, their limited availability and high cost present significant challenges. Non-precious transition metals such as Fe, Co, and Ni have emerged as alternative catalyst materials due to their natural abundance. However, these metals often encounter obstacles related to their hydrogen adsorption behavior. This commentary highlights the various strategies employed to optimize the electronic structures of non-precious metal-based catalysts to enhance the HER performance. The outlook of non-precious metal-based catalysts is bright, with ongoing and future research activities mainly focusing on improving their properties, integrating these catalysts into commercial water electrolysis systems, and improving the scalability for large-scale hydrogen production. The development of high-performance non-precious metal-based catalysts for HER is crucial to future sustainable and efficient hydrogen production in the transition from fossil fuels to clean energy.

N‐Doped Carbon Nanofibers and Carbon Nanotubes‐Encapsulated CoNi Alloy as Highly Active Oxygen Reduction Catalysts for Direct Methanol Fuel Cells

The slow oxygen reduction kinetics of direct methanol fuel cell (DMFCs) are one of the limiting factors affecting its application. Therefore, exploring nonprecious catalysts with high activity and methanol resistance is urgently needed. Herein, zeolitic imidazolate framework‐8 particles are first blended with different proportions of metal salts (Ni as well as Co) and further electrospun to obtain a nanofiber precursor. After pyrolysis treatment, a composite catalyst (CoNi@N‐CNFs) with a highly dispersed CoNi alloy phase supported by porous N‐doped carbon nanofiber and carbon nanotube is prepared. The surface electronic structure can be reasonably adjusted by optimizing the doping ratio of Ni and Co. The CoNi@N‐CNFs shows high oxygen reduction activity and methanol resistance. Half‐wave potential and the onset potential of Co1Ni1@N‐CNFs (Co: Ni mole ratio = 1:1) are 0.79 and 0.87 V. Additionally, Co1Ni1@N‐CNF‐modified DMFC endows a high power density (24.07 mW cm−2), which is close to Pt/C‐based DMFC (27.59 mW cm−2). Rich active sites, large specific surface area, and synergy between CoNi alloy and N configuration of CoNi@N‐CNFs effectively accelerate electron transfer, resulting in the superior catalytic activity. This work provides a new strategy to design effective 1D oxygen reduction reaction catalysts in fuel cells.

A Review of the Structure–Property Relationship of Nickel Phosphides in Hydrogen Production

Hydrogen, one of the most promising forms of new energy sources, due to its high energy density, low emissions, and potential to decarbonize various sectors, has attracted significant research attention. It is known that electrocatalytic hydrogen production is one of the most widely investigated research directions due to its high efficiency in the conversion of electricity to H2 gas. However, given the limited reserves and high cost of precious metals, the search for non-precious metal-based catalysts has been widely explored, for example, transition metal phosphides, oxides, and sulfides. Despite this interest, a detailed survey unveils that the surface and internal structures of the alternative catalysts, including their surface reconstruction, composition, and electronic structure, are poorly studied. As a result, a disconnection in the structure–property relationship severely hinders the rational design of efficient and reliable non-precious metal-based catalysts. In this review, by focusing on Ni5P4, a bifunctional catalyst for water splitting, we systematically summarize the material motifs pertaining to the different synthetic methods, surface characteristics, and hydrolysis properties. It is believed that a cascaded correlation may provide insights toward understanding the fundamental catalytic mechanism and design of robust alternative catalysts for hydrogen production.

Origin of deactivation of aqueous Na–CO2 battery and mitigation for long-duration energy storage

The development of long-duration energy storage technology is crucial to facilitate the efficient utilization of renewable energy sources while mitigating carbon dioxide production. In this study, we investigate the deactivation and reactivation mechanisms of the aqueous Na–CO2 battery during extended cycling. We have designed the cathode to include non-precious intermetallic catalysts. As the cell undergoes repeated cycles, the voltage polarization during discharge progressively rises, eventually leading to the cell's deactivation and formation of decomposition products clogging the electrode surface. Results obtained from comprehensive characterization techniques, including conductive atomic force microscopy (cAFM), Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and inductively coupled plasma-mass spectrometry provide insight into the decomposition products. We also showcase an electrochemical approach for regeneration of these aqueous cells. Our findings, along with the insights we have gained, provide a path toward creating long-duration systems with self-healing properties.

Tungsten doping-Induced electronic structure modulation in NiFe-based metal-organic frameworks for enhanced oxygen evolution reaction

NiFe-based metal-organic frameworks (MOFs) are promising low-cost and easily prepared non-precious catalysts for the oxygen evolution reaction (OER). However, effectively modulating the electronic structures in these electrocatalysts remains a critical challenge. In this study, we successfully incorporated tungsten into FeNi-MOF to synthesize W-doped FeNi2.4-MIL-53 and achieved electronic structure modulation. The results show that the optimized FeNi2.4W0.05-MIL-53 exhibits a lowe overpotential of 235 mV at a current density of 10 mA cm−2, low Tafel slope of 43.3 mV dec−1, and high cyclability over 1000 cycles. Density functional theory (DFT) calculations demonstrate that the conversion from O* to OOH* is the rate-determining step on the active sites of FeNi2.4W0.05-MIL-53. The incorporation of tungsten induces an upshift of the d-band center of the active site, effectively modulating the adsorption energy of oxygen intermediates, thereby enhancing the catalytic activity.

Catalytic CO2 hydrogenation to hydrocarbon fuels in a potassium ion-conducting reactor

The electrochemically assisted CO2 hydrogenation directly to hydrocarbon fuels was studied, apparently for the first time, over a cheap, widespread and non-precious Fe catalyst in a potassium ion conducting (K-β-Al2O3) reactor, under atmospheric pressure, at relatively low temperatures and using representative concentrated CO2 and H2 gas mixtures and an easily scalable tubular catalyst-electrode configuration. The Fe electrocatalytic film was deposited by dip-coating on a commercial K-β-Al2O3 candle and characterized, both as prepared and after activation and testing, by TPR, TGA, XPS, XRD and SEM-EDX. The optimum operating conditions for both Fe activation (300 ºC, 75% H2, 24 hours) and electropromoted CO2 hydrogenation (300 ºC, 1.5 V, H2/CO2=3) were identified. Long-term tests on electrochemically promoted CO2 hydrogenation to hydrocarbons were performed under selected operating conditions to assess electrocatalyst stability. Both the selectivity to the target product (C5+ hydrocarbons) and the stability of the catalyst can be tuned in situ by modifying the potassium surface coverage via electrochemical pumping of potassium ions through the applied polarization. Finally, as an attempt to improve the catalyst-electrode behaviour, powdered catalysts, based on iron nanoparticles dispersed on KVO3 (a K+ and e- co-conductor) with different Fe loadings (17 and 9 wt%) were prepared and comparatively studied for CO2 hydrogenation to hydrocarbons. The catalyst with higher Fe loading was selected as the most promising, in terms of activity, selectivity and stability, for further catalyst-electrode optimisation by deposition, via dip-coating, of a Fe-KVO3 film on the K-β-Al2O3 candle.