Earth-abundant Transition Metals Research Articles

Modification of NiSe2 Nanoparticles by ZIF-8-Derived NC for Boosting H2O2 Production from Electrochemical Oxygen Reduction in Acidic Media

The two-electron oxygen reduction reaction (2e− ORR) has emerged as an attractive alternative for H2O2 production. Developing efficient earth-abundant transition metal electrocatalysts and reaction mechanism exploration for H2O2 production are important but remain challenging. Herein, a nitrogen-doped carbon-coated NiSe2 (NiSe2@NC) electrocatalyst was prepared by successive annealing treatment. Benefiting from the synergistic effect between the NiSe2 nanoparticles and NC, the 2e− ORR activity, selectivity, and stability of NiSe2@NC in 0.1 M HClO4 was greatly enhanced, with the yield of H2O2 being 4.4 times that of the bare NiSe2 nanoparticles. The in situ Raman spectra and density functional theory (DFT) calculation revealed that the presence of NC was beneficial for regulating the electronic state of NiSe2 and optimizing the adsorption free energy of *OOH, which could enhance the adsorption of O2, stabilize the O-O bond, and boost the production of H2O2. This work provides an effective strategy to improve the performance of the transition metal chalcogenide for 2e− ORR to H2O2.

On the Capabilities of Transition Metal Carbides for Carbon Capture and Utilization Technologies.

The search for cheap and active materials for the capture and activation of CO2 has led to many efforts aimed at developing new catalysts. In this context, earth-abundant transition metal carbides (TMCs) have emerged as promising candidates, garnering increased attention in recent decades due to their exceptional refractory properties and resistance to sintering, coking, and sulfur poisoning. In this work, we assess the use of Group 5 TMCs (VC, NbC, and TaC) as potential materials for carbon capture and sequestration/utilization technologies by combining experimental characterization techniques, first-principles-based multiscale modeling, vibrational analysis, and catalytic experiments. Our findings reveal that the stoichiometric phase of VC exhibits weak interactions with CO2, displaying an inability to adsorb or dissociate it. However, VC often exhibits the presence of surface carbon vacancies, leading to significant activation of CO2 at room temperature and facilitating its catalytic hydrogenation. In contrast, stoichiometric NbC and TaC phases exhibit stronger interactions with CO2, capable of adsorbing and even breaking of CO2 at low temperatures, particularly notable in the case of TaC. Nevertheless, NbC and TaC demonstrate poor catalytic performance for CO2 hydrogenation. This work suggests Group 5 TMCs as potential materials for CO2 abatement, emphasizes the importance of surface vacancies in enhancing catalytic activity and adsorption capability, and provides a reference for using the infrared spectra as a unique identifier to detect oxy-carbide phases or surface C vacancies within Group 5 TMCs.

Unlocking the Metalation Applications of TMP-powered Fe and Co(II) bis(amides): Synthesis, Structure and Mechanistic Insights.

Typified by LiTMP and TMPMgCl.LiCl, (TMP=2,2,6,6-tetramethylpiperidide), s-block metal amides have found widespread applications in arene deprotonative metalation. On the contrary, transition metal amides lack sufficient basicity to activate these substrates. Breaking new ground in this field, here we present the synthesis and full characterisation of earth-abundant transition metals M(TMP)2 (M=Fe, Co). Uncovering a new reactivity profile towards fluoroarenes, these amide complexes can promote direct M-H exchange processes regioselectively using one or two of their basic amide arms. Remarkably, even when using a perfluorinated substrate, selective C-H metalation occurs leaving C-F bonds intact. Their kinetic basicity can be boosted by LiCl or NBu4Cl additives which enables formation of kinetically activated ate species. Combining spectroscopic and structural studies with DFT calculations, mechanistic insights have been gained on how these low polarity metalation processes take place. M(TMP)2 can also be used to access ferrocene and cobaltocene by direct deprotonation of cyclopentadiene and undergo efficient CO2 insertion of both amide groups under mild reaction conditions.

Highly efficient Cu-Fe containing prussian blue analogs (PBAs) for excellent electrocatalytic activity towards overall water splitting

Hydrogen generation by water electrolysis is considered a clean, green, and renewable approach for sustainable energy demands and environmental management. The efficient use of earth-abundant transition metal catalysts is cost-effective and limits the usage of noble metal catalysts like IrO2, RuO2, and Pt/C. The PBAs (Prussian Blue Analogs) are a class of transition metal hexacyanoferrates that can be tailored for specific electrochemical reactions. Both iron and copper are well-proven transition metals for catalytic activities owing to their aptitude to achieve much-pronounced reactant transformations under minor circumstances, as well as their environmental friendliness, cyclability, and long-term durability at 10 mA cm−2 in 1.0 M KOH, the greenly synthesized Fe8Cu2CN (PBAs) on NF (Nickel foam) displays a low overpotential of 150 mV (118 mV dec−1) for HER (Hydrogen Evolution Reaction) and 290 mV (112 mV dec−1) for OER (Oxygen Evolution Reaction). Fe8Cu2CN displays ultra-stable behavior (150 h) with a slight current loss of 4.2 % for OER and 3.4 % for HER, respectively. The interaction of Fe, Cu, and CN (cyanide) enhances the rate of reaction kinetics. The designing of a water electrolyzer that delivers 10 mA cm−2 at 1.60 V is made possible with the help of the improved bifunctional catalyst Fe8Cu2CN/NF. The Fe8Cu2CN/NF//Fe8Cu2CN/NF exhibits long-last durability (over 180 h) with a negligible current reduction of 5.4 %. The improved effectiveness of the synthesized catalyst is demonstrated by the solar water splitting at 1.66 V. These findings suggest that Fe8Cu2CN/NF//Fe8Cu2CN/NF can be used to produce large quantities of H2 at very affordable prices.

Tuning NaCo(II) Bimetallic Cooperativity to Perform Co-H Exchange / C-F Bond Activation Processes in Polyfluoroarenes.

Recent advances in cooperative chemistry have shown the potential of heterobimetallic complexes combining an alkali-metal with an earth abundant divalent transition metal for the functionalisation of synthetically relevant aromatic molecules via deprotonative metalation. Pairing sodium with cobalt (II), here we provide an overview of the reactivity of bimetallic [NaCo(HMDS)3] [HMDS = N(SiMe3)2] towards C-H and C-F functionalisation of a wide range of perfluorinated molecules. These studies also uncover the enormous potential of this heterobimetallic base to perform Co-H exchanges with excellent selectivity and exceptional stoichiometric control as well as shedding light on the key role played by the alkali-metal.

Co-N-C axially coordination regulated H2O2 selectivity via water medicated recombination of solute •OH: A new route

The cobalt, earth abundant transition metal, embedded in nitrogen doped carbon material as single atom site (Co-N-C) has been manifested as promising electrochemical oxygen reduction reaction (ORR) catalyst, however the unsatisfying production selectivity has hampered its widespread applications. Herein, the H2O2 selectivity of Co-N-C catalyst has been tailored with Co axial functional groups. Thermodynamically, the selectivity is regulated due to the fine-tuning of the adsorption of the key reaction intermediates (ΔG*OOH), and five functional groups, including −O, –OH, –CN, −CH3 and −SO3, endow the Co-N-C catalyst with superior H2O2 selectivity. Importantly, we unravel a new water medicated recombination of solute •OH reaction pathway for H2O2 production, which was the result of dissociation of *HOOH in explicit water environment. That is, two •OH species reaction in the liquid environment which originated from the creaking of *OOH intermediates due to the weakened O-O bond by the interaction with surrounding water. This study provides foundational understanding for the ORR catalytic mechanism at the electrochemical interface and opens up new avenues for rational design of targeted high efficiency electrocatalysts.

Nanostructured NiMoO4 electrode materials for efficient oxygen evolution reaction

Bifunctional electrocatalysts derived from earth-abundant transition metals are a promising substitute for noble metals in general water electrolysis, but their low activity and short durability limit their application. Herein, a nickel molybdate nanoparticles decorated on nickel foam (NiMoO4/NF NPs) electrode was fabricated by a facile hydrothermal method at three different time intervals (6, 12, and 24 h) and verified for the oxygen evolution reaction (OER). The constructed electrodes exhibited high OER activity in 1.0 M KOH with overpotentials of 315 mV, 290 mV and 320 mV for NiMoO4-6 h, NiMoO4-12 h, and NiMoO4-24 h, respectively. In addition, the NiMoO4-12 h electrodes displayed remarkable durability with a negligible reduction of 1.28 % at a current density of 10 mA cm−2 for 200 h. This research work delivers a new pathway to improve the electrocatalytic behaviour of the catalysts by synergistically moderating the inherent electrical conductivity, efficient surface moieties, and surface reaction.

Molecular and single-atom catalysts based on earth-abundant transition metals for the electroreduction of CO2 to C1

The electrochemical reduction of carbon dioxide driven by renewable energy sources represents a crucial pathway for CO2 conversion and utilization, offering a viable approach for achieving sustainable carbon neutralization. Recent advancements in the design and comprehension of catalytic materials and electrolyte systems have steadily enhanced the performance of CO2 electroreduction (CO2ERR). Among the promising materials for CO2 electroreduction, transition metals, such as manganese, nickel, iron, and cobalt, have gained prominence due to their availability in contrast to expensive noble metals. This review delves into the more recent advances on the utilization of molecular catalysts and single-atom catalysts (SACs) for the conversion of CO2 into carbon monoxide and other C1 molecules. The utilization of catalysts based on organometallic molecular complexes has demonstrated notable efficiency. This approach enables the fine-tuning of the electrical and coordination characteristics of the metal center, thereby enhancing metal utilization, reducing poisoning events, and allowing for selectivity control. While much of the research has traditionally focused on homogeneous CO2 electroreduction, recent years have seen increasing attention towards the heterogenization of molecular catalysts. The main organometallic complexes presented in this review are cobalt and iron porphyrin, cobalt phtalocyanine and manganese bipyridine, anchored on carbon-based electrodes. Moreover, single-atom catalysts have emerged as promising candidates for driving CO2ERR, due to their exceptional performance. Among these catalysts, the single-atom Metal-Nitrogen-Carbon (M-N-C) structure stands out as particularly promising. Additionally, the incorporation of nitrogen, sulfur, and oxygen to dope the carbon support can ensure a uniform distribution of the atomic metal within the catalyst. Here, iron, cobalt and nickel SACs are outlined, presenting diverse support materials and operating conditions. Both SACs and molecular catalysts have demonstrated commendable Faradaic efficiencies, indicating their capability to convert CO2 into CO with a high degree of selectivity. These findings suggest that SACs, with their single-atom configurations, and molecular catalysts, with their tailored molecular structures, offer viable and comparable routes for advancing the CO2ERR.

Challenging Task of Ni-Catalyzed Highly Regio-/Enantioselective Semihydrogenation of Racemic Tetrasubstituted Allenes via a Kinetic Resolution Process.

The first earth-abundant transition metal Ni-catalyzed highly regio- and enantioselective semihydrogenation of racemic tetrasubstituted allenes via a kinetic resolution process as a challenging task was well established. This protocol furnishes expedient access to a diversity of structurally important enantioenriched tetrasubstituted allenes and chiral allylic molecules with high regio-, enantio-, and Z/E-selectivity. Remarkably, this semihydrogenation proceeded with one carbon-carbon double bond of allenes, which was regioselective complementary to the Rh-catalyzed asymmetric version. Deuterium labeling experiments and density functional theory (DFT) calculations were carried out to reveal the reasonable reaction mechanism and explain the regio-/stereoselectivity.

Photoredox matching of earth-abundant photosensitizers with hydrogen evolving catalysts by first-principles predictions.

Photoredox properties of several earth-abundant light-harvesting transition metal complexes in combination with cobalt-based proton reduction catalysts have been investigated computationally to assess the fundamental viability of different photocatalytic systems of current experimental interest. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations using several GGA (BP86, BLYP), hybrid-GGA (B3LYP, B3LYP*), hybrid meta-GGA (M06, TPSSh), and range-separated hybrid (ωB97X, CAM-B3LYP) functionals were used to calculate relevant ground and excited state reduction potentials for photosensitizers, catalysts, and sacrificial electron donors. Linear energy correction factors for the DFT/TD-DFT results that provide the best agreement with available experimental reference results were determined in order to provide more accurate predictions. Among the selection of functionals, the B3LYP* and TPSSh sets of correction parameters were determined to give the best redox potentials and excited states energies, ΔEexc, with errors of ∼0.2eV. Linear corrections for both reduction and oxidation processes significantly improve the predictions for all the redox pairs. In particular, for TPSSh and B3LYP*, the calculated errors decrease by more than 0.5V against experimental values for catalyst reduction potentials, photosensitizer oxidation potentials, and electron donor oxidation potentials. Energy-corrected TPSSh results were finally used to predict the energetics of complete photocatalytic cycles for the light-driven activation of selected proton reduction cobalt catalysts. These predictions demonstrate the broader usefulness of the adopted approach to systematically predict full photocycle behavior for first-row transition metal photosensitizer-catalyst combinations more broadly.

Recent Progress of Transition Metal Selenides for Electrochemical Oxygen Reduction to Hydrogen Peroxide: From Catalyst Design to Electrolyzers Application.

Hydrogen peroxide (H2O2) is a highly value-added and environmental-friendly chemical with various applications. The production of H2O2 by electrocatalytic 2e- oxygen reduction reaction (ORR) has emerged as a promising alternative to the energy-intensive anthraquinone process. High selectivity Catalysts combining with superior activity are critical for the efficient electrosynthesis of H2O2. Earth-abundant transition metal selenides (TMSs) being discovered as a classic of stable, low-cost, highly active and selective catalysts for electrochemical 2e- ORR. These features come from the relatively large atomic radius of selenium element, the metal-like properties and the abundant reserves. Moreover, compared with the advanced noble metal or single-atom catalysts, the kinetic current density of TMSs for H2O2 generation is higher in acidic solution, which enable them to become suitable catalyst candidates. Herein, the recent progress of TMSs for ORR to H2O2 is systematically reviewed. The effects of TMSs electrocatalysts on the activity, selectivity and stability of ORR to H2O2 are summarized. It is intended to provide an insight from catalyst design and corresponding reaction mechanisms to the device setup, and to discuss the relationship between structure and activity.

Post transition metal substituted Keggin-type POMs as thin film chemiresistive sensors for H2O and CO2 detection.

Chemiresitive sensing allows the affordable and facile detection of small molecules such as H2O and CO2. Herein, we report a novel class of Earth-abundant post transition metal substituted Keggin polyoxometalates (POMs) for chemiresistive sensing applications, with conductivities up to 0.01 S cm-1 under 100% CO2 and 65% Relative Humidity (RH).

Mo2C coated with Ni nanoparticles as the cathode catalyst towards efficient hydrogen evolution reaction: an experimental and computational investigation.

Although Mo2C and earth-abundant 3d transition metals are regarded as potential catalysts to replace noble metal catalysts for effective hydrogen evolution reaction, their large-scale application is still inhibited by their own defects. Here, a facile thermal treatment method for nonprecious metal catalysts is developed to prepare a porous Ni/Mo2C composite catalyst. The loading density of Ni nanoparticles on the Mo2C surface has an important effect on the activity of the catalyst. By optimizing the Ni doping ratio, the Ni-40/Mo2C-17 sample exhibits the lowest onset overpotential and lowest overpotential at 10 mA cm-2 in both acidic and alkaline electrolytes, compared to other reported Ni- and Mo2C-based catalysts. In addition, theoretical calculations have also confirmed the synergistic effect between Ni nanoparticles and Mo2C, which can balance the thermodynamics between H adsorption and desorption of H2. This work provides an avenue for designing high-performance water-splitting catalytic materials using low-cost species, which exhibit excellent HER activity in a wide pH range.

First-row transition metal carbonates catalyze the electrochemical oxygen evolution reaction: iron is master of them all.

In pursuing green hydrogen fuel, electrochemical water-splitting emerges as the optimal method. A critical challenge in advancing this process is identifying a cost-effective electrocatalyst for oxygen evolution on the anode. Recent research has demonstrated the efficacy of first-row transition metal carbonates as catalysts for various oxidation reactions. In this study, Earth-abundant first-row transition metal carbonates were electrodeposited onto nickel foam (NF) electrodes and evaluated for their performance in the oxygen evolution reaction. The investigation compares the activity of these carbonates on NF electrodes against bare NF electrodes. Notably, Fe2(CO3)3/NF exhibited superior oxygen evolution activity, characterized by low overpotential values, i.e. Iron is master of them all (R. Kipling, Cold Iron, Rewards and Fairies, Macmillan and Co. Ltd., 1910). Comprehensive catalytic stability and durability tests also indicate that these transition metal carbonates maintain stable activity, positioning them as durable and efficient electrocatalysts for the oxygen evolution reaction.

Transition metal nitride catalysts for selective conversion of oxygen-containing molecules.

Earth abundant transition metal nitrides (TMNs) are a promising group of catalysts for a wide range of thermocatalytic, electrocatalytic and photocatalytic reactions, with potential to achieve high activity and selectivity while reducing reliance on the use of Pt-group metals. However, current fundamental understanding of the active sites of these materials and the mechanisms by which selective transformations occur is somewhat lacking. Recent investigations of these materials from our group and others have utilized probe molecules, model surfaces, and in situ techniques to elucidate the origin of their activity, strong metal-support interactions, and unique d-band electronic structures. This Perspective discusses three classes of reactions for which TMNs have been used as case studies to highlight how these properties, along with synergistic interactions with metal overlayers, can be exploited to design active, selective and stable TMN catalysts. First, studies of the reactions of C1 molecules will be discussed, specifically highlighting the ability of TMNs to activate CO2. Second, the upgrading of biomass and biomass-derived oxygenates over TMN catalysts will be reviewed. Third, the use of TMNs for H2 production via water electrolysis will be discussed. Finally, we will discuss the challenges and future directions in the study of TMN catalysts, in particular expanding on opportunities to enhance fundamental mechanistic understanding using model surfaces, the elucidation of active centers via in situ techniques, and the development of efficient synthesis methods and design principles.

Redox-active ligand promoted multielectron reactivity at earth-abundant transition metal complexes

This review highlights the application of redox-active ligands for achieving substrate activation and reactivity through multielectron transfer at earth-abundant transition metal complexes.

Prussian blue analogues-derived 2D NiCo@C bimetals grown on g-C3N4 as photocatalysts for hydrogen evolution

The development of highly active and stable cocatalysts using earth-abundant transition metals to replace noble metals is important for the application of photocatalytic hydrogen production technology. In this study, two-dimensional (2D) carbon-encapsulated NiCo bimetallic nanosheets (NiCo@C) was designed for the first time as a new co-catalyst to synergistically combine with graphitic carbon nitride (g-C3N4) and promote its hydrogen evolution. The NiCo@C cocatalysts were using an innovative molten salt method by using nickel hexacyanocobaltate Ni3[Co(CN)6]2 (Ni-Co PBA) nanocubes as precursor. The Ni-Co PBA nanocubes undergo dissolution growth and salt templating processes to form bimetallic 2D nanosheets during charring in molten salt media, and combine with 2D g-C3N4 to form NiCo@C/g-C3N4 photocatalyst. The optimized NiCo@C/g-C3N4 photocatalyst significantly improved the H2 evolution activity, and the H2 evolution rate reached 3791.07 μmol·g−1·h−1, which was 5 times higher than that of the particle CoNi/g-C3N4 (636.89 μmol·g−1·h−1). The H2 evolution activity was also comparable to that of the photocatalytic activity of 1.0% Pt/g-C3N4 system, indicating that the earth-abundant NiCo@C can replace noble metal as a cocatalyst to significantly enhance the photocatalytic performance of 2D photocatalysts. The conversion of three-dimensional Ni-Co PBA into carbon-coated 2D metal nanosheets by molten salt-assisted pyrolysis provides a feasible approach to explore the synthesis and design of efficient and robust non-precious metal catalysts.

Mechanisms of Stabilization and Degradation of Transition Metal Oxygen Electroreduction Catalysts with in-Situ Electrochemical Flow Cell ICP-MS

Proton exchange membrane hydrogen fuel cell (PEMFC) deployment is presently limited by the high material cost of oxygen reduction reaction (ORR) electrocatalysts at the cathode. Developing low-cost, earth-abundant alternatives for use in acidic environments presents a material stability challenge, especially for long-term device operation. Platinum (Pt)-based materials are used in typical commercial PEMFC cathode formulations due to their simultaneous high performance and long-term stability despite the prohibitively high material cost. Developing lower-cost, longer-life catalyst materials based on earth abundant transition metals can accelerate the adoption of PEMFC technology. The impact of potential, current density, and local microenvironment has been shown to cause degradation of non-Pt materials but standard ex situ measurements can only probe surface restructuring and cumulative dissolution after operation. Material-specific degradation mechanisms that are strong functions of the operating conditions cannot be ascertained without in situ quantification of material degradation under PEMFC-relevant conditions. Information about the degradation pathways of these non-precious catalysts can assist with material design for devices; however, most efforts towards developing an in-situ understanding of PEMFC cathode catalyst degradation under operating conditions are generally limited to Pt-based materials. Extensive in situ characterization has revealed Pt-specific mechanistic information about corrosion pathways as well as conditions that exacerbate Pt alloy leaching. It has been hypothesized that the Pt degradation processes are related to oxide formation under potential cycling. With this critical in-situ information, Pt conditioning protocols have been developed to enhance material lifetime; however, investigations on non-precious materials are less common. Insights into non-precious catalyst degradation in PEMFC operating conditions are not as well-established but could be essential in enabling low-cost materials for commercial use. There is a need for more insights into a vast array of materials which necessitates the development of faster, preferably benchtop techniques for degradation analysis.In this work, we use an in situ electrochemical flow cell assembly and coupled it with an inductively coupled plasma-mass spectrometer (ICP-MS) to quantify the loss of material in real time for several non-Pt materials under reaction conditions. The flow cell is fed by a peristaltic pump at 2.5 mL/min of gas-saturated acidic electrolyte for optimal mass transport. The cell has a three-electrode configuration with a compression-mounted metal foil working electrode, silver/silver chloride reference electrode, and Pt counter electrode downstream of other components. We evaluate a variety of transition metals across the spectrum of ORR activity: palladium, silver, nickel, copper, manganese, and cobalt. Each metal is tested under oxygen and nitrogen saturation in five electrolytes of identical pH: perchloric acid, sulfuric acid, nitric acid, hydrochloric acid, and hydrobromic acid. This setup allows for nearly real time measurement of ORR kinetics and in situ element-specific dissolution rates as a function of time. With careful design of experimental conditions and controlled variables, we are able to suggest mechanisms of degradation with specific reference to conditions under which material loss occurred such as high/low potential, oxygen-saturated/nitrogen-saturated electrolyte, or faradaic/non-faradaic current. We find some metals are stable under nitrogen-saturated electrolyte but corrode more under oxygen-saturated electrolyte only while ORR active. Furthermore, other metals are stable in nitrogen saturated electrolyte at all tested electrochemical conditions but unstable under oxygen saturated electrolyte but only outside the ORR range, implying that cathodic faradaic processes might be stabilizing the surface at low potentials. This stabilization where a thermodynamically unstable material (based on its Pourbaix diagram) exhibits greater immunity while performing ORR in certain electrolytes could inform the development stability mechanisms that direct the design of next generation, non-precious PEMFC cathode catalyst materials. With combined in situ catalyst stability analysis in five pH 1 electrolytes, we can recommend specific conditions for optimizing activity and stability based on the potential range of operation and the electrolyte composition/saturation. We can also distill mechanistic insights from these experiments by creating models that validate causes of catalyst degradation. These models are built using “graphical causal modeling”, which is a mathematical field that goes beyond correlative predictions by venturing into causal inference. We hope to expand this framework into other electrocatalytic reactions of interest. The in-situ ICP-MS electrochemical flow cell setup exhibits promise for accelerating materials stability analysis for enabling next generation Pt-free ORR electrocatalysts through practical experiments and direct comparability to established electrochemical techniques.

Novel Strategies for Efficient Water Electrolysis

A growing global population in parallel with an increased prosperity seen from a global perspective have raised the need for energy and raw material resources exponentially. These increased needs have led to a number of negative consequences such as pollution, raw material shortages, increasing carbon dioxide levels in the atmosphere, and not least a threatening global warming. Renewable energy will be essential to break the dependence of fossil fuels, but due to the intermittency of renewables a storable non-fossil alternative is needed. Hydrogen represents one of very few sustainable options to store renewable energy on large scale and for seasonal variations. Here, we present novel strategies on water electrolysis driven by photovoltaics, with a focus on the development of state-of the art electrocatalysts based on earth-abundant transition metals, doped with sulphur and phosphor [1]. We show that by tuning parameters such as adsorption energy, morphology and conductance of the electrocatalysts we can achieve solar-to hydrogen efficiency approaching 20 % [2]. We discuss on strategies, mechanisms and challenges in the field of PV-driven electrolysis.[1] Ekspong, J; Larsen, C; Stenberg, J;, Kwong, WL; Wang, J; Zhang, J; Johansson, EM; Messinger, J; Edman, L; Wagberg T, Solar-Driven Water Splitting at 13.8% Solar-to-Hydrogen Efficiency by an Earth-Abundant Electrolyzer, ACS Sustainable Chemistry & Engineering, sc-2021-03565f (acssuschemeng.1c03565). (2021)[2] H Zhang, A Aierke, Y Zhou, Z Ni, L Feng, A Chen, T Wågberg, G Hu, A high‐performance transition‐metal phosphide electrocatalyst for converting solar energy into hydrogen at 19.6% STH efficiency, Carbon Energy, 5 (1), e217 (2022)

MOF-Derived Trifunctional High Entropy Sulfides as an Electrocatalyst for Alkaline Unitized Regenerative Fuel Cell Application

Electrochemical devices such as electrolyzers (EL), fuel cells (FC), metal-air batteries (MAB), and unitized regenerative fuel cells (URFC) are key components in our drive toward a renewable energy-based power infrastructure. The potential scale of these devices requires the usage of catalytic materials that exhibit not only excellent catalytic activity but also commendable durability. Conventional precious metal catalysts such as Pt, Ir, Rh, Ru, and Pd are utilized for variable deployments during electrocatalysis. 1 Recent trends in alloying, tuning the band structure, nanosizing of particles, and application of earth-abundant transition metals, have immensely increased the economic feasibility and practical applications of a new genre of electrochemical devices. 2 Here, strategically designed materials, such as metal-organic frameworks (MOF), offers a new route for synthesizing the alloys and their derivatives with high porosities and excellent catalytic activity. 3 High entropy alloys (HEA) containing multiple (four or more) components of metallic oxides, sulfides, and phosphides have emerged as a new class of materials. Effects such as lattice distortion, entropy stabilization, cocktail effect, and formation of multiple oxidation states in such HEA enable access to multiple catalytic centers for catalyzing more than one small molecule activation reaction. 4 The current work focuses on the synthesis of FeCuCoMnNi-based high entropy sulfide (HES) via a unique MOF route. This HES material successfully demonstrates three distinct catalytic reactions: oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The surface morphology and phase of the HES can be critically curated via sulfurizing the multi-metal MOF precursor, which was monitored with a battery of surface characterization techniques. This HES displayed an impressive bifunctionality index of 0.80 V and 1.87 V for application in alkaline URFC (ORR/OER) and EL (HER/OER), where moderate to low overpotentials were observed for OER (η OER = 380 mV), ORR (η ORR = 420 mV), and HER (η HER = 260 mV). The superior electrochemical performance of this HES is attributed to the surface reconstruction mechanism upon the inclusion of transition metals such as Fe, Co, and Mn to Ni leading to the formation of the key Ni-OOH layer. Along with excellent performance, the HES exhibited good durability at +1.5 V vs. RHE up to 12 hours while retaining ~75% of the initial current density, indicating the presence of a high configurational entropy in the material. References Huynh, M., Ozel, T., Liu, C., Lau, E. C., & Nocera, D. G. 2017 Chemical science, 8(7), 4779-4794.Xu, J., Li, J., Xiong, D., Zhang, B., Liu, Y., Wu, K. H., ... & Liu, L. 2018 Chemical science, 9(14), 3470-3476.Karmakar, A., Kumar, N., Samanta, P., Desai, A. V., & Ghosh, S. K. 2016 Chemistry–A European Journal, 22(3), 864-868.Miracle, D. B., Miller, J. D., Senkov, O. N., Woodward, C., Uchic, M. D., & Tiley, J. 2014 Entropy, 16(1), 494-525 Figure 1