Catalysts For Water Electrolysis Research Articles

Cerium-doped Nickel SulfideNanospheres as EfficientCatalysts for Overall Water Splitting.

The development of non-precious metal electrocatalysts with excellent activity and durability for electrochemical water splitting has always been a goal. Transition metal sulfides are attractive electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction(OER). In this article, we designed and constructed efficient catalysts with multiple synergistic interactions and synthesized Ce-NiS2@NFnanosphere using a solvothermal method. Ce-NiS2@NF exhibits excellent HER performance, OER performance, and overall water splitting capability in alkaline electrolytes, demonstrating good stability. The addition of Ce influences the activity of the catalysts, attributed to the synergistic interactions creating more active sites and higher intrinsic activity through the introduction of Ce heteroatoms. Additionally, the self-supported conductive substrate promotes electron transfer, enhancing the intrinsic activity and active site density of the catalyst.This study provides an in-depth investigation into structural design and performance enhancement, offering ideas for designing efficient catalysts for overall water electrolysis. This work provides an in-depth study in terms of structural design performance enhancement and provides ideas for designing efficient alkaline bifunctional catalysts. Valuable insights have been provided in elucidating the intrinsic mechanism of the catalytic activity of cerium-doped nickel sulfidenanospheres,thus providing new guidance in the field of energy conversion technology.

Review—Self-Supporting Electrocatalysts for HER in Alkaline Water Electrolysis

Abstract Hydrogen is a prime candidate for replacing fossil fuels. Electrolyzing water to produce hydrogen stands out as a particularly clean method, garnering significant attention from researchers in recent years. Among the various techniques for electrolyzing water to produce hydrogen, alkaline electrolysis holds the most promise for large-scale industrialization. The key to advancing this technology lies in the development of durable and cost-effective electrocatalysts for the hydrogen evolution reaction (HER). Self-supporting electrode is an electrode structure in which a catalyst layer is formed directly on a substrate (such as carbon cloth, nickel foam, stainless steel, etc.) without using a binder and with good structural stability. In contrast to traditional nanocatalysts, self-supporting electrocatalysts offer significant advantages, including reduced resistance, enhanced stability, and prolonged usability under high currents. This paper reviews recent advancements in HER electrochemical catalysts for alkaline water electrolysis, focusing on the utilization of hydrogen-evolving catalysts such as metal sulfides, phosphides, selenides, oxides, and hydroxides. With self-supported electrocatalysts as the focal point, the paper delves into progress made in their preparation techniques, structural design, understanding of reaction mechanisms, and strategies for performance enhancement. Ultimately, the future development direction of promoting hydrogen evolution by self-supported electrocatalysts in alkaline water electrolysis is summarized.

Performance Evaluation and Durability Analysis of NiFeCoOx Catalysts for Alkaline Water Electrolysis in Anion Exchange Membrane Electrolyzers

Performance Evaluation and Durability Analysis of NiFeCoOx Catalysts for Alkaline Water Electrolysis in Anion Exchange Membrane Electrolyzers

Constructing quasi‐amorphous cobalt oxyhydroxide nanowires with synergy of anion and cation via ion exchange reconstruction for large-current–density oxygen generation

Deep insight into the synergy between anion and cation aids in the maximization of catalytic activity and the rational exploitation of efficient oxygen-evolving catalysts. However, how to use ion exchange reconstruction to devise highly active and cost-efficient oxygen evolution reaction (OER) catalysts with anion and cation synergies for water electrolysis is rarely reported. Herein, the cobalt triphosphide (CoP3) nanowires are elaborately devised as a component-flexible precatalyst for directing an anodic reconfiguration with Ni cation exchange to construct a highly active and quasi‐amorphous cobalt oxyhydroxide (CoOOH) catalyst integrated with cation (Ni) substitution and oxyanion (PO43-) decoration (denoted by R-(Ni)CoP3). Interestingly, the structural evolution and the Ni cation exchange processes are captured through various in/ex situ techniques. The resultant R-(Ni)CoP3 nanowires display a splendid activity with low overpotentials of 406 and 420 mV to respectively deliver industrial grade current densities of 1000 and 1500 mA cm−2, and an outstanding stability over 300 h at a large current density of 500 mA cm−2, superior to most progressive cobalt-based OER materials and the benchmark IrO2. The combination of theoretical calculations with experimental studies demonstrate that the synergy of cation (Ni) substitution and oxyanion (PO43-) decoration can significantly modulate the electronic states of CoOOH and optimize the adsorption free energy of OER intermediates, thus immensely expediting the kinetics process and enhancing the charge transfer ability and the intrinsic OER activity. This research suggests ion-regulatory reconfiguration as a flexible and changeable strategy to construct various efficient and advanced catalysts for water electrolysis and beyond.

Iron-Doped carbon supported nickel selenide heterogeneous materials for Dual-Function water electrolysis catalysts

Developing efficient, economical, and resource-abundant dual-function electrocatalysts for water splitting is crucial. In this study, uniform growth of NiSex nanocrystals on Fe-doped XC-72 carbon (NS/XC-Fe) was achieved through a solvothermal method, resulting in the formation of a composite material with outstanding performance. NS/XC-Fe exhibits excellent catalytic performance for both oxygen evolution reaction (OER) (261 mV, 10 mA·cm−2) and hydrogen evolution reaction (HER) (275 mV, 10 mA·cm−2) under alkaline conditions, owing to the introduction of iron and the construction of heterogeneous interfaces. Additionally, NS/XC-Fe exhibited excellent stability during the 24 h polarization test. Density Functional Theory (DFT) calculations indicated that the introduction of iron optimized the catalyst’s H adsorption capability, while the construction of heterogeneous interfaces lowered the energy barrier of the rate-determining step. This demonstrates the significant potential of NS/XC-Fe as an electrocatalyst, providing new insights for the design and synthesis of efficient bifunctional electrochemical water splitting catalysts.

Large-Scale and Simple Synthesis of NiFe(OH)x Electrode Derived from Raney Ni Precursor for Efficient Alkaline Water Electrolyzer

Water electrolysis is a crucial technology in the production of hydrogen energy. Due to the escalating industrial demand for green hydrogen, the required electrode size for a traditional alkaline water electrolyzer has been increasing. Numerous studies have focused on developing highly active oxygen evolution reaction (OER) catalysts for water electrolysis. However, there remains a significant gap between the microscale synthesis of catalysts in laboratory settings and the macroscale preparation required for industrial scenarios. This challenge is particularly pronounced in the synthesis of sizable self-supported electrodes. In this work, we employed a commercially available Raney Ni-coated Ni mesh as a precursor material to fabricate a self-supported NiFe(OH)x@Raney Ni anode with a substantial dimension exceeding 300 mm through a straightforward immersion technique. The as-prepared electrode exhibited remarkable electrocatalytic OER activity, as an overpotential of only 240 mV is required to achieve 10 mA cm−2. This performance is comparable to that of NiFe-LDHs synthesized via a hydrothermal method, which is difficult to scale up for industrial applications. Furthermore, the electrode demonstrated exceptional durability, maintaining stable operation for over 100 h at a current density of 500 mA cm−2. The large-scale electrode displayed consistent overpotentials across various areas, indicating uniform catalytic activity. When integrated into an alkaline water electrolysis device, it delivered an average cell voltage of 1.80 V at 200 mA cm−2 and achieved a direct current hydrogen production energy consumption as low as 4.3 kWh/Nm3. These findings underline the suitability of electrodes for industrial scale applications, offering a promising alternative for energy-efficient hydrogen production.

Mn-doped Sequentially Electrodeposited Co-based Oxygen Evolution Catalyst for Efficient Anion Exchange Membrane Water Electrolysis.

Designing high-performance and durable oxygen evolution reaction (OER) catalysts is important for green hydrogen production through anion exchange membrane water electrolysis (AEMWE). Herein, a series of Mn-doped Co-based OER catalysts supported on FeOxHy (FCMx) are presented to enhance the OER activity. Mn doping effectively reduces the size of the Co oxide particles, thereby augmenting the active surface area. Moreover, Mn doping induces the creation of oxygen vacancies, leading to an efficient structural conversion during the OER, which is confirmed via in situ Raman spectroscopy. Under optimal conditions, the catalyst exhibits an overpotential of 234.4 mV at 10 mA cm-2 and a Tafel slope of 37.2 mV dec-1 under half-cell conditions. The AEMWE single-cell system demonstrates a current density of 1560 mA cm-2 at 1.8 V at 60 °C with a degradation rate of 0.4 mV h-1 for 500 h at 500 mA cm-2. Our development of a robust OER catalyst represents notable progress in the field of nonprecious-metal water electrolysis, marking a step toward cost-effective green hydrogen production.

High‐Efficiency Iridium‐Yttrium Alloy Catalyst for Acidic Water Electrolysis

AbstractProton exchange membrane (PEM) water electrolysis holds great promise in revolutionizing clean energy production by enabling the efficient generation of hydrogen. Nevertheless, a formidable challenge persists in the realm of designing electrocatalysts that are both highly active and acid‐resistant during the oxygen evolution reaction (OER), thereby mitigating the substantial kinetic barrier. In this study, the facile synthesis of iridium‐yttrium (IrY) alloy nanocatalysts via a thermal shock method is introduced, which exhibits exceptional activity in the context of acidic water oxidation. Through the strategic incorporation of dispersed Y into the lattice of Ir metal, the IrY catalyst demonstrates a notably low overpotential of 255 mV at a current density of 10 mA cm−2 and showcases remarkable catalytic stability in acidic electrolytes, enduring for over 500 h with a high current density of 100 mA cm−2. Through a comprehensive set of in situ characterizations and analytical methods, the formation of a surface Ir‐based oxide layer, induced by deprotonation and electrochemical oxidation is unveiled, which is notably stabilized by the presence of Y dopants. This stabilization of the active site imparts enhanced resistance to over‐oxidation and dissolution, underpinning the exceptional stability of the catalyst. Theoretical calculations suggest that the incorporation of Y into the catalyst structure has a significant impact on enhancing the reactivity of the oxygen intermediate (O*) at adjacent Ir sites, thus lowering the overpotential and promoting OER activity. The alloying approach presents a straightforward method for achieving atomic‐level modifications in catalyst design and can pave the way for the development of more effective and economically viable OER catalysts and beyond.

Fe–Ni-doped metal-organic framework derived CoSe2 as an efficient and stable electrocatalyst for hydrogen evolution reaction

The development of efficient, stable and low-cost catalysts for hydrogen evolution reaction (HER) is one of the major difficulties in water electrolysis. It is also the key to realizing the large-scale production of hydrogen energy, a renewable and clean energy source. In recent years, metal-organic frameworks (MOFs) have attracted much attention as novel precursors for preparing water electrolysis catalysts due to their high porosity and large specific surface area. In this paper, we use ZIF-67 as a precursor and modify it by doping transition metal elements Fe and Ni. Afterwards, Fe–Ni–CoSe2@NC is synthesized by a thermal selenization process. The results show that the HER overpotential of the catalyst after modification is reduced by 50%, and the efficiency of water electrolysis is significantly improved. Moreover, the catalyst has good stability under alkaline condition and is more economical than the expensive Pt-based catalysts, which provides more possibilities for industrial applications.

Janus electronic state of supported iridium nanoclusters for sustainable alkaline water electrolysis

Metal-support electronic interactions play crucial roles in triggering the hydrogen spillover (HSo) to boost hydrogen evolution reaction (HER). It requires the supported metal of electron-rich state to facilitate the proton adsorption/spillover. However, this electron-rich metal state contradicts the traditional metal→support electron transfer protocol and is not compatible with the electron-donating oxygen evolution reaction (OER), especially in proton-poor alkaline conditions. Here we profile an Ir/NiPS3 support structure to study the Ir electronic states and performances in HSo/OER-integrated alkaline water electrolysis. The supported Ir is evidenced with Janus electron-rich and electron-poor states at the tip and interface regions to respectively facilitate the HSo and OER processes. Resultantly, the water electrolysis (WE) is efficiently implemented with 1.51 V at 10 mA cm–2 for 1000 h in 1 M KOH and 1.44 V in urea-KOH electrolyte. This research clarifies the Janus electronic state as fundamental in rationalizing efficient metal-support WE catalysts.

Self-standing Ni–Cu–Ti/NCNTs electrocatalyst with porous structure for hydrogen evolution reaction

The development of water electrolysis hydrogen production technology is of great significance for accelerating the global carbon neutrality goals. Nickel-based electrode materials are considered the most promising catalysts for alkaline water electrolysis. However, the slow kinetics of the hydrogen evolution reaction remains a key challenge to be solved. To address this, a porous Ni–Cu–Ti/NCNTs cathode electrode was prepared using the powder metallurgy method. The microstructure characterizations and electrochemical measurements revealed that adjusting the content of NCNTs, while maintaining the Ni–Cu–Ti ratio of 5.5:3.5:1, can improve the catalytic activity of hydrogen evolution to a certain extent. Among the electrodes tested at room temperature, the one with 0.7% NCNT content exhibited the best performance in terms of hydrogen evolution. The analysis suggests that the porous structure of the electrode provides ample channels for object transmission. The addition of NCNTs further enhances the surface roughness of the electrode, exposing more active sites. Additionally, NCNTs promote electron transfer, synergize with Ni, Cu, and Ti, and improve the catalytic activity of hydrogen evolution.

Enhanced stability of bipolar membrane water electrolysis with FeCoNi layered double hydroxides electrocatalyst in a frequently-inverted electrolyte mode

The aim of this study was to synthesize a novel, non-noble metal-based layered double hydroxides (LDH) bifunctional catalyst for bipolar membrane water electrolysis (BPMWE) and to improve the stability of BPMWE with forward bias BPM. The FeCoNi-LDH/NF catalyst was successfully prepared using an electrodeposition method and tested in BPMWE. Low overpotentials for both the HER and OER were observed in the FeCoNi-LDH/NF electrode. Significant changes in pH and conductivity occurred in the anolyte and catholyte of BPMWE without frequently-inverted electrolyte within 192 h, resulting in an increase of cell voltage for hydrogen production. However, in the frequently-inverted electrolyte mode, where the electrolyte was periodically shifted every 24 h, excess H+ in the anolyte and OH– in the catholyte of BPMWE were effectively neutralized by electrolyte shifting, resulting in stable pH and conductivity in the electrolytes and maintaining a stable cell voltage within 192 h. With 1 M KOH as the electrolyte, the cell voltage of BPMWE was only 1.58 V under a current density of 20 mA·cm−2 at 90 °C. Our study should provide insights into efficient bifunctional catalyst synthesis and operational stability control in BPMWE.

Synthesis of nickel phosphate nanowires as a bifunctional catalyst for water electrolysis in alkaline media

The electrocatalytic water splitting (WS) process for hydrogen (H2) and oxygen (O2) production is known for its high efficiency, necessitating the development of bifunctional electrode materials. These materials must possess strong catalytic activity, significant active sites, high stability, and an abundance of earth-friendly components to ensure efficient and prolonged H2 and O2 generation. In this study, we employed a hydrothermal method to synthesize unique one-dimensional (1D) nickel phosphate (NiPO) nanoneedles directly grown on nickel foam (NF). The in-situ synthesis of the NiPO/NF catalyst offers favorable streamlining, facilitating electrode production and improving the contact between active sites and the conductive substrate. Under alkaline conditions, the NiPO/NF electrodes demonstrated low overpotentials of 374 mV and 377 mV at a high current density (J) of 250 mAcm−2 for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. These values indicate efficient and stable electrocatalytic activity. Moreover, the NiPO/NF catalyst exhibited continuous bifunctional catalytic activity for 12 hours with a J exceeding 20 mAcm−2. These findings suggest that NiPO/NF has the potential to be a cost-effective and sustainable option for large-scale WS applications.

Tungsten pnictides for water electrolysis: advances and perspectives

AbstractHydrogen fuel is recognized as a promising energy carrier for the sustainable development of global energy system and the green hydrogen production via water electrolysis attracts great interest. The development of cost-effective electrocatalysts for water electrolysis is important for enhancing green hydrogen production efficiency. Recently, tungsten pnictides (phosphides and nitrides) have emerged as promising catalysts for water electrolysis, and efficient tungsten pnictide-based catalysts with different nanostructures, compositions, and surface chemical properties have been developed. In this review, recent progress in the design of tungsten pnictide-based electrocatalysts for water electrolysis is comprehensively analyzed. The synthesis of tungsten pnictide-based electrocatalysts are discussed briefly. Then, current achievements in developing efficient tungsten pnictide electrocatalysts for water electrolysis are detailed, and four key catalyst design strategies (i.e., nanostructure control, heteroatom doping, defect engineering, and heterostructure design) are outlined. The physicochemical properties-catalytic performance relationship of tungsten pnictide-based electrocatalysts is also discussed. At last, perspectives in this field are put forward for guiding further research on the design and application of high-performance tungsten pnictide-based electrocatalysts.

Orbital Occupancy Modulation to Optimize Intermediate Absorption for Efficient Electrocatalysts in Water Electrolysis and Zinc-Ethanol-Air Battery.

Spin engineering is a promising way to modulate the interaction between the metal d-orbital and the intermediates and thus enhance the catalytic kinetics. Herein, an innovative strategy is reported to modulate the spin state of Co by regulating its coordinating environment. o-c-CoSe2 -Ni is prepared as pre-catalyst, then in situ electrochemical impedance spectroscopy (EIS)and in situ Raman spectroscopy are employed to prove phase transition, and CoOOH/Co3 O4 is formed on the surface as active sites. In hybrid water electrolysis, the voltage has a negative shift, and in zinc-ethanol-air battery, the charging voltage is lowered and the cycling stability is greatly increased. Coordinated atom substitution and crystalline symmetry change are combined to regulate the absorption ability of reaction intermediates with balanced optimal adsorption. Coordinated atom substitution weakens the adsorption while the crystalline symmetry change strengthens the adsorption. Importantly, the tetrahedral sites are introduced by Ni doping which enables the co-existence of four-coordinated sites and six-coordination sites in o-c-CoSe2 -Ni. The dz2 + dx2 -y2 orbital occupancy decreases after the atomic substitution, while increases after replacing the CoSe6 -Oh field with CoSe6 -Oh /CoSe4 -Td . This work explores a new direction for the preparation of efficient catalysts for water electrolysis and innovative zinc-ethanol-air battery.

Optimizing the intermediates adsorbability and revealing the dynamic reconstruction of Co6Fe3S8 solid solution for bifunctional water splitting

Co9S8 has been extensively studied as a promising catalyst for water electrolysis. Doping Co9S8 with Fe improves its oxygen evolution reaction (OER) performance by regulating the catalyst self-reconfigurability and enhancing the absorption capacity of OER intermediates. However, the poor alkaline hydrogen evolution reaction (HER) properties of Co9S8 limit its application in bifunctional water splitting. Herein, we combined Fe doping and sulfur vacancy engineering to synergistically enhance the bifunctional water-splitting performance of Co9S8. The as-synthesized Co6Fe3S8 catalyst exhibited excellent OER and HER characteristics with low overpotentials of 250 and 84 mV, respectively. It also resulted in the low Tafel slopes of 135 mV dec−1 for the OER and 114 mV dec−1 for the HER. A two-electrode electrolytic cell with Co6Fe3S8 used as both the cathode and anode produced a current density of 10 mA cm−2 at a low voltage of only 1.48 V, maintaining high stability for 100 h. The results of in/ex-situ experiments indicated that the OER process induced electrochemical reconfiguration, forming CoOOH/FeOOH active species on the catalyst surface to enhance its OER performance. Density functional theory (DFT) simulations revealed that Fe doping and the presence of unsaturated coordination metal sites in Co6Fe3S8 promoted H2O and H* adsorption for the HER. The findings of this study can help develop a strategy for designing highly efficient bifunctional water splitting electrocatalysts.

Dual doping: An emerging strategy to construct efficient metal catalysts for water electrolysis

AbstractDeveloping efficient electrocatalysts for water electrolysis is critical for sustainable hydrogen energy development. For enhancing the catalytic performance of metal catalysts, dual doping has attracted enormous interest for its high effectiveness and facile realization. Dual doping is effective for tuning the electronic properties, enhancing the electrical conductivity, populating active sites, and improving the stability of metal catalysts. In this review, recent developments in cation–cation, cation–anion, and anion–anion dual‐doped catalysts for water splitting are comprehensively summarized and discussed. An emphasis is put on illustrating how dual doping regulates the external and internal properties and boosts the catalytic performance of catalysts. Additionally, perspectives are pointed out to guide future research on engineering high‐performance heteroatom‐doped electrocatalysts.

Cactus-like NC/CoxP electrode enables efficient and stable hydrogen evolution for saline water splitting

Designing efficient and robust catalysts for hydrogen evolution reaction (HER) is imperative for saline water electrolysis technology. A catalyst composed of CoxP nanowires array with N-doped carbon nanosheets (NC) was fabricated on Ni foam (NF) by an in-situ growth strategy. The material is designated as NC/CoxP@NF. In the preparation process, Co(OH)2 nanowires were transformed into a metal organic framework of cobalt (ZIF-67) on NF by the dissolution-coordination of endogenous Co2+ and 2-methylimidazole. The resulting cactus-like microstructure gives NC/CoxP@NF abundant exposed active sites and ion transport channels, which improve the HER catalytic reaction kinetics. Furthermore, the interconnected alternating nanowires and free-standing nanosheets in NC/CoxP@NF improve its structural stability, and the formation of surface polyanions (phosphate) and a NC nanosheet protective layer improve the anti-corrosive properties of catalysts. Thus, the NC/CoxP@NF has an excellent performance, requiring overpotentials of 107 and 133 mV for HER to achieve 10 mA cm−2 in 1.0 mol L−1 KOH and 1.0 mol L−1 KOH + 0.5 mol L−1 NaCl, respectively. This in-situ transformation strategy is a new way of constructing highly-efficient HER catalysts for saline water electrolysis.

Constructing an oxide-fluoride heterojunction supported on carbon cloth as a highly active and stable catalyst for enhancing overall water-splitting

To realize large-scale production of hydrogen by water electrolysis, the development of inexpensive and high-performance catalysts is urgently needed. Herein, we developed an oxide-fluoride (Co3O4–CoF2) heterojunction catalyst with mooncake shape morphology supported on carbon cloth (CC) used as a bifunctional water electrolysis catalyst in 1 M KOH. The obtained Co3O4–CoF2 heterojunction exhibits a preferable kinetic process and more active sites than its mono components Co3O4 and CoF2, which only needs 46 mV for HER and 169 mV for OER at 10 mA cm−2 comparable to benchmark Pt/C and even super to benchmark IrO2. Meanwhile, it also demonstrates long-term stability, maintaining activity for 100 h for both HER and OER. Importantly, when assembled as a water electrolysis device, only a low cell voltage of 1.45 V is required to achieve the current density of 10 mA cm−2. Meanwhile, it can output continuous and stable current densities of 10, 100, and 10 mA cm−2 approaching 24 h under constant cell voltages of 1.47, 1.69, and 1.47 V, respectively. Therefore, the oxide-fluoride heterojunction catalyst unambiguously is a type of ideal bifunctional water electrolysis catalyst in alkaline media.

Water- Surface reconstruction of sulfurized spinel-structured oxide oxygen catalysts for alkaline water electrolysis

Slow kinetics related to oxygen evolution reactions (OERs) are currently the main obstacle in developing effective and extremely stable oxygen electrocatalysts for alkaline water electrolysis cells. Catalysts based on spinel-structured...