Solvothermal synthesis of iron phosphides and their application for efficient electrocatalytic hydrogen evolution

In this paper, we present a solvothermal synthesis of iron phosphide electrocatalysts using a triphenylphosphine (TPP) precursor. The synthetic protocol generates Fe₂P phase at 300 °C and FeP phase at 350 °C. To enhance the catalytic activities of obtained iron phosphide particles heat-treatments were carried out at elevated temperatures. Annealing at 500 °C under reductive atmosphere induced structural changes in the samples: (i) Fe₂P provided a pure Fe₃P phase (Fe₃P−500 °C) and (ii) FeP transformed into a mixture of iron phosphide phases (Fe₂P/FeP−500 °C). Pure Fe₂P films was prepared under argon atmosphere at 450 °C (Fe₂P−450 °C). The electrocatalytic activities of heat-treated Fe₂P−450 °C, Fe₃P−500 °C, and Fe₂P/FeP−500 °C catalysts were studied for hydrogen evolution reaction (HER) in 0.5 M H₂SO₄. The HER activities of the iron phosphide catalyst were found to be phase dependent. The lowest electrode potential of 110 mV vs. a reversible hydrogen electrode (RHE) at 10 mA cm⁻² was achieved with Fe₂P/FeP−500 °C catalyst.     

Extraordinarily high hydrogen-evolution-reaction activity of corrugated graphene nanosheets derived from biomass rice husks

The metal-free carbonaceous catalysts are one of the promising candidates for efficient electrocatalytic hydrogen production. Aiming at demonstrating the high electrocatalytic activity of the hydrogen evolution reaction (HER), we synthesized the biomass rice husk-derived corrugated graphene (RH-CG) nanosheets via the KOH activation. The 700 °C-activated RH-CG nanosheets exhibited the large specific surface area as well as the high electrical conductivity. When using the RH-CG nanosheets as a HER electrocatalyst in 0.5 M H₂SO₄, the excellent HER activities with a small overpotential (9 mV at 10 mA/cm²) and a small Tafel slope (31 mV/dec) were achieved. The results provide a new strategy for materializing the superb biomass-derived electrocatalyst for highly efficient hydrogen production.     

Autogenous growth of highly active bifunctional Ni–Fe2B nanosheet arrays toward efficient overall water splitting

Developing an effective and low-cost bifunctional electrocatalyst for both OER and HER to achieve overall water splitting is remaining a challenge to meet the needs of sustainable development. Herein, an electroless plating method was employed to autogenous growth of ultrathin Ni–Fe₂B nanosheet arrays on nickel foam (NF), in which the whole liquid phase reduction reaction took no more than 20 min and did not require any other treatments such as calcination. In 1.0 M KOH electrolyte, the resulted Ni–Fe₂B ultrathin nanosheet displayed a low overpotential of 250 mV for OER and 115 mV for HER to deliver a current density of 10 mA cm^?2, and both OER and HER activities remained stable after 26 h stability testing. Further, the couple electrodes composed of Ni–Fe₂B could afford a current density of 10 mA cm^?2 towards overall water splitting at a cell voltage of 1.64 V in 1.0 M KOH and along with excellent stability for 26 h. The outstanding electrocatalytic activities can be attributed to the synergistic effect of electron-coupling across Ni and Fe atoms and active sites exposed by large surface area. The effective combination of low cost and high electrocatalytic activity brings about a promising prospect for Ni–Fe₂B nanosheet arrays in the field of overall water splitting.     

Co3O4–C@FeMoP on nickel foam as bifunctional electrocatalytic electrode for high-performance alkaline water splitting

Exploring low-cost, highly efficient, and sustainable non-precious electrocatalysts for electrolytic H₂ generation is driving research for the sustainable green urban development. Herein, we present a simple synthetic approach, through a two-step process, to prepare the bifunctional electrode of Co₃O₄–C@FeMoP hybrid micro rods/nanosheets anchored on nickel foam (NF), in which the Co₃O₄–C microrods grown on NF surface are decorated by FeMoP nanosheet layers, which is directly grown through a simple hydrothermal followed by post-phosphorization processes. The obtained hybrid hierarchical Co₃O₄–C@FeMoP/NF shows a significant enhancement in the electrocatalytic activities of oxygen/hydrogen evolution reactions (OER/HER) in comparison to the individual Co₃O₄–C and FeMoP nanostructures, thanks to more heterointerface active sites provided by FeMoP nanostructures with three-dimensional (3-D) layered architectures. The Co₃O₄–C@FeMoP/NF catalyst exhibits a relatively small overpotential of 200 mV vs. RHE for OER to achieve 20 mA/cm² and 123 mV vs RHE at 10 mA/cm² for HER along with excellent durability in alkaline electrolytes. We demonstrate the bifunctional electrocatalytic electrode as the electrolyzer for the generation of H₂ via water splitting at small applied voltage of 1.61 V to achieve 10 mA/cm² and good stability for 24-h continuous running.     

Porous NiFe alloys synthesized via freeze casting as bifunctional electrocatalysts for oxygen and hydrogen evolution reaction

Binder-free NiFe-based electrocatalyst with aligned pore channels has been prepared by freeze casting and served as a bifunctional catalytic electrode for oxygen and hydrogen evolution reaction (OER and HER). The synergistic effects between Ni and Fe result in the high electrocatalytic performance of porous NiFe electrodes. In 1.0 M KOH, porous Ni₇Fe₃ attains 100 mA cm⁻² at an overpotential of 388 mV with a Tafel slope of 35.8 mV dec⁻¹ for OER, and porous Ni₉Fe₁ exhibits a low overpotential of 347 mV at 100 mA cm⁻² with a Tafel slope of 121.0 mV dec⁻¹ for HER. The Ni₉Fe₁//Ni₉Fe₁ requires a low cell voltage of 1.69 V to deliver 10 mA cm⁻² current density for overall water splitting. The excellent durability at a high current density of porous NiFe electrodes has been confirmed during OER, HER and overall water splitting. The fine electrocatalytic performances of the porous NiFe-based electrodes owing to the three-dimensionally well-connected scaffolds, aligned pore channels, and bimetallic synergy, offering excellent charge/ion transfer efficiency and sizeable active surface area. Freeze casting can be applied to design and synthesize various three-dimensionally porous non-precious metal-based electrocatalysts with controllable multiphase for energy conversion and storage.     

Superhydrophilic 3D peony flower-like Mo-doped Ni2S3@NiFe LDH heterostructure electrocatalyst for accelerating water splitting

Constructing highly efficient nonprecious electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is essential to improve the efficiency of overall water splitting, but still remains lots of obstacles. Herein, a novel 3D peony flower-like electrocatalyst was synthesized by employing Mo–Ni₂S₃/NF nanorod arrays as scaffolds to in situ growth ultrathin NiFe LDH nanosheets (Mo-Ni₂S₃@NiFe LDH). As expected, the novel peony flower-like Mo–Ni₂S₃@NiFe LDH displays superior electrocatalytic activity and stability for both OER and HER in alkaline media. Low overpotentials of only 228 mV and 109 mV are required to achieve the current densities of 50 mA cm^?2 and 10 mA cm^?2 for OER and HER, respectively. Additionally, the material remarkably accelerates water splitting with a low voltage of 1.54 V at 10 mA cm^?2, which outperforms most transition metal electrodes. The outstanding electrocatalytic activity benefits from the following these features: 3D peony flower-like structure with rough surface provides more accessible active sites; superhydrophilic surfaces lead to the tight affinity between electrode with electrolyte; metallic Ni substrate and highly conductive Mo–Ni₂S₃ nanorods scaffold together with offer fast electron transfer; the nanorod arrays and porous Ni foam accelerate gas bubble release and ions transmission; the strong interfacial effect between Mo-doped Ni₃S₂ and NiFe LDH shortens transport pathway, which are benefit for electrocatalytic performance enhancement. This work paves a new avenue for construction and fabrication the 3D porous structure to boost the intrinsic catalytic activities for energy conversion and storage applications.     

Improved energy conversion and storage performance enabled by hierarchical zigzag-like P-doped CuCo2O4 nanosheets based 3D electrode materials

Developing a bi-functional material which can meet both electrochemical water splitting and supercapacitors (SCs) is a hot spot in current research. In this study, hierarchical zigzag-like phosphorus doped CuCo₂O₄ nanosheets based 3D electrode materials were successfully synthesized via a hydrothermal method and followed by thermal treatment. Since the unique morphology of 2D nanosheets with zigzag-like edges could provide more reactive sites, which is not only conducive to the hydrogen evolution reaction (HER), but also conducive to the electrochemical energy storage. Meanwhile, the doping of phosphorus was adopted to improve the conductivity, which would further enhance the electrochemical properties of CuCo₂O₄. Thereafter, its performance for HER and SCs in 1 M KOH were systematically investigated. As an electrode for HER, it only required a low overpotential of 152 mV to reach 10 mA cm^?2 with a Tafel slope of 115.7 mV dec^?1. Furthermore, I-t test result showed an excellent stability. As an electrode for SCs, it exhibited a high specific capacity of 896.9C g^?1 at 1 A g^?1 in three-electrode system. All in all, the obtained hierarchical zigzag-like phosphorus doped CuCo₂O₄ nanosheets provided a feasible route for the design of bi-functional electrode materials both for energy conversion and storage.     

Engineering Ru nanoparticles embedded in 2D N-doped carbon nanosheets decorated with 2D Fe3O4–Fe3C heterostructures for efficient hydrogen evolution in alkaline and acidic media

Tailoring surface composition and structures of catalysts affects their catalytic performance in hydrogen evolution reaction owing to the geometric and electronic effects. Herein, Ru nanoparticles embedded in 2D N-doped carbon nanosheets decorated with 2D Fe₃O₄–Fe₃C heterostructures (Ru/Fe₃O₄–Fe₃C/NC) are fabricated via pyrolysis of the mixture containing 2D-Fe₂O₃ nanosheets, dopamine hydrochloride, RuCl₃·xH₂O, and melamine. Interestingly, the good hydrogen evolution behavior is achieved on Ru/Fe₃O₄–Fe₃C/NC with the high reactivity and stability. Ru/Fe₃O₄–Fe₃C/NC offers an overpotential of 141 mV to realize the current density of 10 mA/cm² in 0.5 mol/L (M) H₂SO₄ electrolyte. As for 1 M KOH, Ru/Fe₃O₄–Fe₃C/NC promotes hydrogen evolution reactivity with 148 mV to achieve 10 mA/cm². The current density slightly degrades after continuous I-t tests, verifying the good stability for Ru/Fe₃O₄–Fe₃C/NC. The high reactivity might stem from high dispersion of Ru nanoparticles, enhanced conductivity due to doping N into carbon nanosheets, and heterointerfaces between Fe–O and Fe–C.     

Effect of rGO on Fe2O3–TiO2 composite incorporated NiP coating for boosting hydrogen evolution reaction in alkaline solution

Fe₂O₃–TiO₂ composite incorporated NiP coating is a known promising catalytic coating for electrocatalytic Hydrogen Evolution Reaction (HER). It is explored in the present study that the activity of the coating can be enhanced by incorporation of rGO. The Fe₂O₃–TiO₂/rGO, electrocatalyst is synthesized by a facile hydrothermal method. Various compositions of the Fe₂O₃–TiO₂/rGO incorporated NiP coatings on mild steel substrate are developed by a chemical reduction method. The developed Fe₂O₃–TiO₂/rGO composite coating exhibits effective hydrogen evolution reaction activity with a Tafel slope of 98 mV dec⁻¹ and a low overpotential of 96 mV at a current density of 10 mA cm⁻². The hydrogen evolution reaction mechanism comprises of Volmer (adsorption of Hydrogen atom) followed by Heyrovskii (reduction to H₂). The enhanced catalytic activity by the incorporation of rGO into the coating is due to three dimensional projections of nano Fe₂O₃–TiO₂ on the folded surface of rGO. It effectively enhances the electrochemically active surface area of the coated electrode. The electrode is highly stable during alkaline HER. These results reveal that Fe₂O₃–TiO₂/rGO can be treated as an effective electrocatalyst during HER from alkaline solutions. The conclusions pave the way for exploration of new similar catalysts for other applications.     

Exposure of active sites in Mn–SnS2 nanosheets to boost hydrogen evolution reaction

Designing and synthesizing high-activity, durable, and low-cost catalysts for the electrochemically transformation of water to hydrogen are vitally important to future energy systems. Herein, a simple but effective strategy for manganese-metal-heteroatom doping is adopted to intrinsically elevate the electrocatalytic activities of SnS₂ nanosheets by a facile two steps hydrothermal-sulfurization approach. Electrocatalytic hydrogen evolution (HER) performance of Mn–SnS₂ nanosheets grown on 3D nickel foam (Mn–SnS₂/NF) is efficiently optimized since the dopants and defects endow the Mn–SnS₂/NF vast active sites. An overpotential as low as 71 mV is required to drive a current density of 10 mA/cm² with a low Tafel slope of 72 mV dec^?1 in alkaline environment (1 M KOH). In addition, the Mn–SnS₂/NF exhibits prominent stability in 1 M KOH electrolyte, which is an indispensable index for the potential HER electrocatalysts. The present work demonstrates that the heteroatom manganese doping strategy renders a meaningful route for synthesizing cost-efficient HER electrocatalysts in alkaline condition.     

Fabrication of phosphorus-mediated MoS2 nanosheets on carbon cloth for enhanced hydrogen evolution reaction

Molybdenum sulfide (MoS₂) as a graphene-like sheet material has attracted wide attention owing to the potential for hydrogen evolution reaction (HER). However, the large-scale application of MoS₂ is still difficult due to the inherent poor conductivity and insufficient active edge sites. Herein, we develop a simple method to grow P-doped MoS₂ nanosheets on carbon cloth for high efficiency HER. The 2D carbon cloth can prevent the stacking of MoS₂ nanosheets and improve the conductivity with the doping of P atoms. As a result, the P–MoS₂/CC-300 shows the excellent electrocatalytic activity with an overpotential of 81 mV at 10 mA cm^?2 and the lower Tafel slope of 98 mV/dec. Furthermore, it also shows the good electrocatalytic durability for 15 h. This work provides an opportunity for the design of excellent and robust MoS₂-based catalyst via structural engineering and doping method.     

Tungsten promoted nickel phosphide nanosheets supported on carbon cloth: An efficient and stable bifunctional electrocatalyst for overall water splitting

It is of great significance to develop a highly active, durable and inexpensive bifunctional electrocatalyst for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report a tungsten-doped nickel phosphide nanosheets based on carbon cloth (W–Ni₂P NS/CC) as an efficient bifunctional catalyst through simple hydrothermal and phosphorization for overall water splitting in 1 M KOH. The W–Ni₂P NS/CC exhibits excellent electrochemical performance with low overpotentials for HER (η₁₀ = 71 mV, η₅₀ = 160 mV) and OER (η₂₀ = 307 mV, η₅₀ = 382 mV) in 1 M KOH, as well as superior long-term stability. Moreover, W–Ni₂P NS/CC as a bifunctional catalyst reveals remarkable activity with a low voltage of 1.55 V to reach a current density of 20 mA cm⁻². This work provides a viable bifunctional catalyst for the overall water splitting.     

Engineering of molybdenum sulfide nanostructures towards efficient electrocatalytic hydrogen evolution

Water splitting is an appealing way of producing hydrogen fuel, which requires efficient and affordable electrode materials to make the overall process viable. In the last couple years, abundant transition metals (and their compounds and hybrids) attracted ever-growing attention as the alternatives of noble metals. Particularly the layered transition metal dichalcogenide (TMDs) are interesting with their stability and promising electrocatalytic performance for hydrogen evolution reaction (HER). However, the neat TMDs are often poor in terms of the abundance of catalytically active sites and electrical conductivity, which limit their application potential significantly. Herein, as a proof-of-concept, we report on the design of a high-performance electrocatalyst system formed by the decoration of ultrasmall molybdenum sulfide (MoS₂) nanosheets on carbon nanotubes (CNTs). The ultrasmall MoS₂ nanosheets provide distorted lattice, confined size and rich defects, which endows the resulting electrocatalysts (MoS₂/CNT) with abundant active sites. The CNTs, on the other hand, serve as the conductive net for ensuring electrocatalytic performance. As a result, the hybrid electrocatalyst exhibits excellent electrocatalytic performance for HER, achieving a large current density of 100 mA cm⁻² at overpotential of only 281 mV and a small Tafel slope of 43.6 mV dec⁻¹ along with a decent stability. Our results are of high interest for electrocatalyst technologists as well as hydrogen fuel researchers.     

Investigation of the electrocatalytic performance for oxygen evolution reaction of Fe-doped lanthanum nickelate deposited on pyrolytic graphite sheets

Perovskite-type metal oxides have emerged as important materials in renewable energy because the high electrocatalytic performance for oxygen evolution reaction (OER). Hence, we perform a study on the electrocatalytic properties of LaNi_1-xFe_xO₃ (x = 0.0, 0.3, 0.6, and 0.9 mol%) for OER, mainly analyzing the influence provoked by the incorporation of Fe³⁺ in the lattice as well as the use of pyrolytic graphite sheet (PGS) as a potential substrate for electrocatalysis. These perovskites were synthesized by the co-precipitation method. The thin film electrodes were prepared depositing the obtained powders on PGS substrates via drop-casting. Depending on the Fe³⁺ level, structural changes and morphological modifications were identified for these materials. The highest electrocatalytic activity for OER was detected for LaNi_0.4Fe_0.6O₃. Besides the low charge transfer resistance, LaNi_0.4Fe_0.6O₃ exhibited a lower overpotential (439 mV) and a smaller Tafel slope (52 mV dec⁻¹) than the LaNiO₃ (465 mV and 76 mV dec⁻¹).     

Porous sunflower plate-like NiFe2O4/CoNi–S heterostructure as efficient electrocatalyst for overall water splitting

Constructing high-efficient and nonprecious electrocatalysts is of primary importance for improving the efficiency of water splitting. Herein, a novel sunflower plate-like NiFe₂O₄/CoNi–S nanosheet heterostructure was fabricated via facile hydrothermal and electrodeposition methods. The as-fabricated NiFe₂O₄/CoNi–S heterostructure array exhibits remarkable bifunctional catalytic activity and stability toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. It presents a small overpotential of 219 mV and 149 mV for OER and HER, respectively, to produce a current density of 10 mA cm^?2. More significantly, when the obtained electrodes are used as both the cathode and anode in an electrolyzer, a voltage of 1.57 V is gained at 10 mA cm^?2, with superior stability for 72 h. Such outstanding properties are ascribed to: the 3D porous network structure, which exposes more active sites and accelerates mass transfer and gas bubble emission; the high conductivity of CoNi–S, which provides faster charge transport and thus promotes the electrocatalytic reaction of the composites; and the effective interface engineering between NiFe₂O₄ (excellent performance for OER) and CoNi–S (high activity for HER), which leads to a shorter transport pathway and thus expedites electron transfer. This work provides a new strategy for designing efficient and inexpensive electrocatalysts for water splitting.     

NiMo/Cu-nanosheets/Ni-foam composite as a high performance electrocatalyst for hydrogen evolution over a wide pH range

We designed and fabricated non-precious and highly efficient electrocatalysts of nickelmolybdenum/copper-nanosheets/nickel-foam composites (NiMo/Cu-NS/NF) by step electrodepositions, combining with chemical oxidation method. The catalysts were charaterized by means of SEM, XRD and XPS spectra. Their electrocatalytic activities were assessed by hydrogen evolution reactions (HER) over a wide pH range, where acidic, neutral and alkaline electrolytes were used, respectively. Benefiting from the unique midlayer Cu nanosheets (NS) architecture and optimum Mo–Ni composition at the surface layer which led to high electronic conductivity and large electrochemically active surface area (ECSA), the NiMo/Cu-NS/NF-2 catalyst displayed superior electrocatalytic activities with low overpotentials of η₁₀ = 43, 86 and 89 mV in 0.5 M H₂SO₄, 1.0 M PBS and 1.0 M KOH electrolyte, respectively. Especially in the acidic condition, it exhibited the best electrocatalytic activity with smaller Tafel slope of 54 mV dec^?1 and higher exchange current density of 1.93 mA cm^?2.     

Ti3C2Tx nanosheets with uniformly anchored Ru nanoparticles for efficient acidic and basic hydrogen evolution reaction

Developing an efficient and stable electrocatalyst for hydrogen evolution reaction (HER) remains critically signi?cance for renewable hydrogen production. Herein, a facile electrochemical reduction method was proposed to fabricate Ru nanoparticles (NPs) evenly anchored on Ti₃C₂T_x nanosheets (Ti₃C₂T_x-NS) electrocatalyst (Ru@Ti₃C₂T_x-NS). Interestingly, owing to the interaction between Ru NPs and Ti₃C₂T_x-NS, the resultant Ru@Ti₃C₂T_x-NS electrocatalyst performed a Pt-like electrocatalytic property for HER under the acidic solution with an ultra-low overpotential of 46.75 mV to reach ?10 mA/cm², a small Tafel slope of 30.6 mV/dec, and long-term stability. Simultaneously, the Ru@Ti₃C₂T_x-NS also displayed splendid HER electrocatalytic performance in the basic condition. Furthermore, Ru@Ti₃C₂T_x-NS showed a lower value of Gibbs free energy for HER (?0.21 eV) than either pure Ru or Ti₃C₂T_x-NS from the theoretical calculation results. It is expected that such a promising approach would be extended to design and fabricate other noble metal NPs anchored MXene nanosheets for HER application.     

A bottom-up method to construct Ru-doped FeP nanosheets on foam iron with ultra-high activity for hydrogen evolution reaction

As a clean, high calorific value and renewable energy, hydrogen is considered to be an ideal green energy to replace traditional fossil energy. Among various methods for preparing hydrogen, electrolytic water hydrogen evolution has attracted the attention of researchers because of its high efficiency, easy separation of products and green and pollution-free advantages. In this experiment, starting from the porous foam iron, Fe₂O₃ nanosheets are obtained by anodic oxidation, and then the material is phosphated by in-situ phosphating in a tubular furnace to obtain FeP nanosheets. Finally, the Ru dopants are deposited into the lattice of FeP nanosheets by electrodeposition to obtain the Ru-doped FeP nanosheets. Through the characterization of morphology and the test of electrocatalytic hydrogen evolution performance, the Ru-doped FeP nanosheets show ultra-high electrochemical hydrogen evolution activity and have regular nanosheets array structure.     

Phosphorus-doped Fe3O4 nanoflowers grown on 3D porous graphene for robust pH-Universal hydrogen evolution reaction

It is extremely necessary to develop highly efficient and low-cost non-noble metal electrocatalysts for hydrogen evolution reaction (HER) under a pH-universal condition in the realm of sustainable energy. Herein, we have successfully prepared phosphorus doped Fe₃O₄ nanoflowers on three-dimensional porous graphene (denoted as P–Fe₃O₄@3DG) via a simple hydrothermal and low-temperature phosphating reaction. The P–Fe₃O₄@3DG hybrid composite not only demonstrates superior performance for HER in 1.0 M KOH with low overpotential (123 mV at 10 mA/cm²), small Tafel slope (65 mV/dec), and outstanding durability exceeding 50 h, but also exhibits satisfying performances under neutral and acidic medium as well. The 3D graphene foam with large porosity, high conductivity, and robust skeleton conduces to more active sites, and faster electron and ion transportation. The phosphorus dopant provides low Gibbs free energy and ability of binging H⁺. The synergistic effect of 3DG substrate and P–Fe₃O₄ active material both accelerates the catalytic activity of Fe-based hybrid composite for HER.     

Co3S4 nanosheets on Ni foam via electrodeposition with sulfurization as highly active electrocatalysts for anion exchange membrane electrolyzer

Co₃S₄ nanosheets on Ni foam (NS/NF) were prepared by sulfurization for various time after calcination of electrodeposited Co(OH)₂. In our FE-SEM images, we observed that Co₃S₄ NS was vertically, or obliquely, deposited on the Ni foam. As a result, the structure contained more active sites, and active sites were highly accessible to the electrolyte for the hydrogen evolution reaction (HER). Furthermore, results of XPS and XRD analysis confirmed S-conversion from Co₃O₄ to Co₃S₄ during sulfurization. 3-Co₃S₄ NS/NF with sulfurization for 3 h exhibited the highest sulfur content, while Co₃S₄ began to desulfurize to Co₉S₈ after sulfurization for 4 h. The 3-Co₃S₄ NS/NF electrocatalyst showed a lowest overpotential of 93 mV at −10 mA/cm², with a Tafel slope of −55.1 mV/dec in N₂-purged 1 M KOH. Also, the single cell anion exchange membrane water electrolyzer (AEMWE) showed a high current density of 431 mA/cm² with cell voltage 2.0 V_cell at 40–45 °C.