Facile fabrication of flower-like CuS/MnCO3 microspheres clusters on nickel foam as an efficient bifunctional catalyst for overall water splitting

Utilizing the abundant elements on earth to product inexpensive, high-active and stable catalysts for water splitting is very significant but still remains serious challenge to produce hydrogen. Herein, heterostructures of CuS/MnCO₃ on nickel foam substrate are firstly successfully synthesized via a facile one-step hydrothermal strategy. The as-prepared electrocatalyst displays an enhanced oxygen evolution reaction (OER) performance in alkaline conditions with a minimum overpotential of 70 mV and a small Tafel slope of 42.5 mV/dec to achieve 10 mA cm^?2. The catalyst also exhibits an excellent HER activity with a low overpotential of 143 mV and the Tafel slope of 51.4 mV/dec to acquire 10 mA cm^?2 in 1.0 M KOH. Moreover, when the CuS/MnCO₃//CuS/MnCO₃ electrode is applied for the overall water splitting, the electrolyzer cell device affords 10 mA cm^?2 at a relative low voltage of 1.43 V, which is one of the best catalysts ever reported. In stability test, its activity first decreases and then remains stable in 1 M KOH solution for about 10 h, indicating that the electrode has good electrochemical stability. Density functional theory calculations (DFT) show that MnCO₃ has a stronger adsorption energy for water than CuS does, indicating that MnCO₃ is a real active center and CuS plays a certain synergistic effect. This work not only provides a low-cost and efficient bifunctional catalyst for water splitting technology, but also extends the application of bifunctional catalyst based on transition metal sulfide and carbonate compound.     

Co-based MOF-derived Co/CoN/Co2P ternary composite embedded in N- and P-doped carbon as bifunctional nanocatalysts for efficient overall water splitting

In this work, we developed ternary metallic cobalt-cobalt nitride-dicobalt phosphide composite embedded in nitrogen and phosphorus co-doped carbon (Co/CoN/Co₂P-NPC) as bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The as-prepared Co/CoN/Co₂P-NPC is achieved by simultaneous annealing and phosphating of a Co–N rich metal-organic frameworks (MOFs) precursor. Compare with the phosphorus-free Co/CoN embedded nitrogen-doped carbon electrocatalyst (Co/CoN-NC), the as-prepared Co/CoN/Co₂P-NPC display superior HER and OER low overpotential of 99 mV and 272 mV at current density of 10 mA cm⁻². When Co/CoN/Co₂P-NPC electrocatalyst is use as bifunctional catalysts in overall alkaline water splitting, it exhibit excellent behaviour with 10 mA cm⁻² current at overall cell potential of 1.60 V. The excellent performance of Co/CoN/Co₂P-NPC electrocatalyst is attributed to the phosphating process that could further enhance synergistic effect, create stronger electronic interactions, and form efficient dual heteroatom doping to optimize the interfacial adhesion within the electrocatalyst. This present work will create more opportunities for the development of new, promising and more active sites electrocatalysts for alkaline electrolysis.     

Ni3S2-MoSx nanorods grown on Ni foam as high-efficient electrocatalysts for overall water splitting

In order to solve the problem of large overpotential in water electrolysis for hydrogen production, transition metal sulfides are promising bifunctional electrocatalysts for hydrogen evolution reaction/oxygen evolution reaction that can significantly reduce overpotential. In this work, Ni₃S₂ and amorphous MoS_x nanorods directly grown on Ni foam (Ni₃S₂-MoS_x/NF) were prepared via one-step solvothermal process, which were used as a high-efficient electrocatalyst for overall water splitting. The Ni₃S₂-MoS_x/NF composite exhibits very low overpotentials of 65 and 312 mV to reach 10 mA cm⁻² and 50 mA cm⁻² in 1.0 M KOH for HER and OER, respectively. Besides, it exhibits a low Tafel slope (81 mV dec⁻¹ for HER, 103 mV dec⁻¹ for OER), high exchange current density (1.51 mA cm⁻² for HER, 0.26 mA cm⁻² for OER), and remarkable long-term cycle stability. This work provides new perspective for further the development of highly effective non-noble-metal materials in the energy field.     

MoS2/NiFeS2 heterostructure as a highly efficient electrocatalyst for overall water splitting at high current densities

Searching for efficient, stable and low-cost nonprecious catalysts for oxygen and hydrogen evolution reactions (OER and HER) is highly desired in overall water splitting (OWS). Herein, presented is a nickel foam (NF)-supported MoS₂/NiFeS₂ heterostructure, as an efficient electrocatalyst for OER, HER and OWS. The MoS₂/NiFeS₂/NF catalyst achieves a 500 mA cm⁻² current density at a small overpotential of 303 mV for OER, and 228 mV for HER. Assembled as an electrolyzer for OWS, such a MoS₂/NiFeS₂/NF heterostructure catalyst shows a quite low cell voltage (≈1.79 V) at 500 mA cm⁻², which is among the best values of current non-noble metal electrocatalysts. Even at the extremely large current density of 1000 mA cm⁻², the MoS₂/NiFeS₂/NF catalyst presents low overpotentials of 314 and 253 mV for OER and HER, respectively. Furthermore, MoS₂/NiFeS₂/NF shows a ceaseless durability over 25 h with almost no change in the cell voltage. The superior catalytic activity and stability at large current densities (>500 mA cm⁻²) far exceed the benchmark RuO₂ and Pt/C catalysts. This work sheds a new light on the development of highly active and stable nonprecious electrocatalysts for industrial water electrolysis.     

Petal-like NiCoP sheets on 3D nitrogen-doped carbon nanofiber network as a robust bifunctional electrocatalyst for water splitting

Searching high-active, stable and abundant bifunctional catalysts to replace noble metals for hydrogen and oxygen evolution reactions (HER and OER) is desired. Herein, petal-like NiCoP sheets were synthesized on carbon paper covered with a 3D nitrogen-doped carbon nanofiber network (NiCoP/CNNCP) by a simple hydrothermal process followed by phosphorization. The HER overpotential in 0.5 M H₂SO₄ and OER overpotential in 1 M KOH of the NiCoP/CNNCP electrode only required 55 mV and 260 mV to drive a current density of 10 mA cm^?2, respectively, which was comparable or even better than most nickel-and cobalt-based phosphide catalysts. The overall water-splitting electrolyzer with an asymmetric electrolyte system assembled using NiCoP/CNNCP as bifunctional electrodes required an extremely low cell voltage of 1.04 V to achieve a current density of 10 mA cm^?2, which was much lower than almost all alkaline electrolysis systems.     

Electrodeposition of NiS/Ni2P nanoparticles embedded in amorphous Ni(OH)2 nanosheets as an efficient and durable dual-functional electrocatalyst for overall water splitting

To develop earth-abundant and cost-effective catalysts for overall water splitting is still a major challenge. Herein, a unique “raisins-on-bread” Ni–S–P electrocatalyst with NiS and Ni₂P nanoparticles embedded in amorphous Ni(OH)₂ nanosheets is fabricated on Ni foam by a facile and controllable electrodeposition approach. It only requires an overpotential of 120 mV for HER and 219 mV for OER to reach the current density of 10 mA cm⁻² in 1 M KOH solution. Employed as the anode and cathode, it demonstrates extraordinary electrocatalytic overall water splitting activity (cell voltage of only 1.58 V @ 10 mA cm⁻²) and ultra-stability (160 h @ 10 mA cm⁻² or 120 h @50 mA cm⁻²) in alkaline media. The synergetic electronic interactions, enhanced mass and charge transfers at the heterointerfaces facilitate HER and OER processes. Combined with a silicon PV cell, this Ni–S–P bifunctional catalyst also exhibits highly efficient solar-driven water splitting with a solar-to-hydrogen conversion efficiency of 12.5%.     

A nano-spherical structure Ni3S2/Ni(OH)2 electrocatalyst prepared by one-step fast electrodeposition for efficient and durable water splitting

Developing non-noble metal catalysts with excellent electrocatalytic performance and stability is of great significance to hydrogen production by water electrolysis, but there are still problems of low activity, complex preparation and high cost. Herein, we fabricated a novel Ni₃S₂/Ni(OH)₂ dual-functional electrocatalyst by a one-step fast electrodeposition on nickel foam (NF). While maintaining the electrocatalytic performance of Ni₃S₂, the existence of heterostructure and Ni(OH)₂ co-catalyst function greatly improves the overall water splitting performance of Ni₃S₂/Ni(OH)₂–NF. Hence, It shows a low overpotential of 66 mV at 10 mA cm^?2 for HER and 249 mV at 20 mA cm^?2 for OER. The dual-functional electrocatalyst needs only 1.58 V at 20 mA cm^?2 when assembled two-electrode electrolytic cell. Impressively, the electrocatalyst also shows outstanding catalytic stability for about 800 h when 20 and 50 mA cm^?2 constant current was applied, respectively which demonstrates a potential electrocatalyst for overall water splitting.     

Multi-active site CoNi-MOFs as non-noble bifunctional electrocatalysts for highly efficient overall water splitting

The high-efficiency non-precious metal catalysts for oxygen evolution (OER) and hydrogen evolution (HER) are of great significance to the development of renewable energy technologies. Herein, a multiple active sites CoNi-MOFs-DBD electrocatalyst modified by low temperature plasma (DBD) was successfully synthesized by converting metal hydroxyfluoride on nickel foam into a well-arranged MOFs array using vapor deposition. The as-prepared CoNi-MOFs-DBD electrode showed better HER and OER catalytic activity, super hydrophilicity, and excellent stability. In an alkaline medium, the overpotential of HER is 203 mV at 10 mA cm^?2 and that of OER is 168 mV at 40 mA cm^?2. When CoNi-MOFs-DBD was used as a bifunctional electrocatalyst for overall water splitting in a two-electrode system, a current density of 10 mA cm^?2 can be achieved at a low voltage of 1.42 V, which shows great potential in electrocatalytic water splitting.     

Bimetallic metal-organic framework derived electrocatalyst for efficient overall water splitting

The development of bifunctional catalysts that can be applied to both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is widely regarded as a key factor in the production of sustainable hydrogen fuel by electrochemical water splitting. In this work, we present a high-performance electrocatalyst based on nickel-cobalt metal-organic frameworks for overall water splitting. The as-obtained catalyst shows low overpotential to reaches the current density of 10 mA cm⁻² with 249 mV for OER and 143 mV for HER in alkaline media, respectively. More importantly, when the electrolyzer was assembled with the as-prepared catalyst as anode and cathode simultaneously, it demonstrates excellent activity just applies a potential of 1.68 V to achieve 10 mA cm⁻² current density for overall water splitting.     

Bifunctional electrocatalysts for water splitting from a bimetallic (V doped-NixFey) Metal–Organic framework MOF@Graphene oxide composite

An ongoing challenge still lies in the exploration of proficient electrocatalysts from earth-abundant non-precious metals instead of noble metal-based catalysts for clean hydrogen energy through large-Scale electrochemical water splitting. However, developing a non-precious transition metals based, stable electrocatalyst for cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) is important challenge for modern energy conversion technology. In this report Vanadium doped bimetallic nickel-iron nanoarray, fabricated by carbon supported architecture through carbonization process for electrochemical water splitting. Three types of catalysts were prepared in different molar ratio of Ni/Fe. The electrocatalytic performance demonstrated that the catalyst with equal mole ratio (0.06:0.06) of Ni/Fe possess high catalytic activity for both OER and HER in alkaline and acidic medium. Besides, our findings revealed that the doping of vanadium could play a strong synergetic effect with Ni/Fe, which provide a small overpotential of 90 mV and 210 mV at 10 mA cm^?2 for HER and OER respectively compared to the other two catalyst counterparts. Also, the catalyst with 1:1 (Ni/Fe) molar ratio showed a high current density of 208 mA cm^?2 for HER at 0.5 M H₂SO₄ and 579 mA cm^?2 for OER at 1 M KOH solution, the both current densities are much higher than the other two catalysts (different Ni/Fe ratio). In addition, the presented catalysts showed extremely good durability, reflecting in more than 20 h of consistent Chronoamprometry study at fixed overpotential η = 250 mV without any visible voltage elevation. Similarly, the (Ni/Fe) equal ratio catalyst showed better corrosion potential 0.209 V vs Ag/AgCl and lower current density 0.594 × 10^?12 A cm^?2 in high alkaline medium. The V-doping, MOF/GO surface defects are significantly increased the corrosion potential of the V-Ni_xFe_y-MOF/GO electrocatalyst. Besides, the water electrolyzed products were analysed by gas chromatography to get clear insights on the formed H₂ and O₂ products.     

Preparation of NiCo-LDH@NiCoV-LDH interconnected nanosheets as high-performance electrocatalysts for overall water splitting

Alkaline water electrolysis is a promising strategy for the production of hydrogen and oxygen. However, developing high-efficiency non-precious electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is still a big challenge. Here, we report a nickel foam-based electrode coated with NiCoV-LDH and NiCo-LDH nanosheets (denoted as NiCo-LDH@NiCoV-LDH/NF) by a two-step method for efficient water splitting performance. The NiCo-LDH@NiCoV-LDH/NF with unique nanosheet-on-nanosheet construction can enlarge the electrochemical active specific surface area greatly, and thus accelerate the charge transfer of electrocatalytic reactions. Besides, the doping of vanadium could also improve the OER performance. The electrode only requires a low overpotential for OER (260 mV at 100 mA cm^?2), and HER (80 mV at 10 mA cm^?2) reactions in 1.0 mol/L KOH solution at room temperature. Furthermore, in the two-electrode water splitting test, a current density of 10 mA cm^?2 was achieved at 1.55 V using 1.0 mol/L KOH solution, with excellent durability of 40 h. This work provided a facile method for developing new bifunctional catalysts.     

Niobium-doped cobalt phosphide nanowires realizing enhanced electrocatalytic activity for overall water splitting

Designing cost-effective bifunctional catalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline electrolyte remains a significant challenge. Herein, we report adding Nb to pristine CoP nanowires enhances the material's catalytic activities towards HER and OER. Density functional theory (DFT) calculation unravels that the Nb atoms not only optimize hydrogen binding abilities on CoP surface, but also modulate the surface electron densities of in situ formed β-CoOOH during anodic oxidation, thereby greatly accelerate both the HER and OER kinetics in alkaline solutions. In addition, an alkaline electrolyzer using Nb-doped CoP nanowires as cathode and anode for overall water splitting, delivers 100 mA cm^?2 at low cell voltage of 1.70 V, superior to Pt//RuO₂ couple. This doping strategy can be extended to other transition metal phosphides as multifunctional catalysts towards overall water splitting and beyond.     

Bifunctional nanoporous ruthenium-nickel alloy nanowire electrocatalysts towards oxygen/hydrogen evolution reaction

A class of ruthenium-nickel alloy catalysts featured with nanoporous nanowires (NPNWs) were synthesized by a strategy combining rapid solidification with two-step dealloying. RuNi NPNWs exhibit excellent electrocatalytic activity and stability for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in which the RuNi-2500 NPNWs catalyst shows an OER overpotential of 327 mV to deliver a current density of 10 mA cm^?2 and the RuNi-0 NPNWs catalyst requires the overpotential of 69 mV at 10 mA cm^?2 showing the best HER activity in alkaline media. Moreover, the RuNi-1500 NPNWs catalyst was used as the bifunctional electrocatalyst in a two-electrode alkaline electrolyzer for water splitting, which exhibits a low cell voltage of 1.553 V and a long-term stability of 24 h at 10 mA cm^?2, demonstrating that the RuNi NPNWs catalysts can be considered as promising bifunctional alkaline electrocatalysts.     

Tailoring cation vacancies in Co,Ni phosphides for efficient overall water splitting

High-efficiency water splitting catalysts are competitive in energy conversion and clean energy production. Herein, a bifunctional water splitting catalyst CoNiP with cation vacancy defects (CoNiP–V) is constructed through defect engineering. The results show that abundant cation vacancy defects in CoNiP–V are bifunctional active centers in the process of water electrolysis, which enhance the activity of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). In 1.0 mol L^?1 potassium hydroxide, CoNiP–V requires a pretty low overpotential of 58 mV to reach a geometrical current density of 10 mA cm^?2 for HER. To deliver a current density of 100 mA cm^?2, only 137 mV and 340 mV of overpotential are needed for HER and OER, respectively. Moreover, the cell with CoNiP–V as both cathode and anode exhibits good stability, which only needs 1.61 V to achieve a current density of 100 mA cm^?2, and the cell voltage barely rises 10% after 100 h’ test under 100 mA cm^?2. Therefore, CoNiP–V is promising for the development of efficient water splitting catalysts.     

Facile construction of well-defined hierarchical NiFe2O4/NiFe layered double hydroxides with a built-in electric field for accelerating water splitting at the high current density

Interfacial charge redistribution induced by a strong built-in electric field can expertly optimize the adsorption energy of hydrogen and hydroxide for improving the catalytic activity. Herein, we develop a well-defined hierarchical NiFe₂O₄/NiFe layered double hydroxides (NFO/NiFe LDH) catalysts, exhibiting superior performance due to the strong interfacial electric field interaction between NiFe₂O₄ nanoparticle layers and NiFe LDH nanosheets. In 1 M KOH, NFO/NiFe LDH needs 251 mV and 130 to drive 50 and 10 mA cm^?2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Moreover, only 1.517 V cell voltage is needed to reach 10 mA cm^?2 towards overall water splitting. Notably, under simulated industrial electrolysis conditions, NFO/NiFe LDH only needs 289 mV to drive 1000 mA cm^?2. This work puts a deep insight into the role of the built-in electric field in transition metal-based catalysts for accelerating water splitting and scalable industrial electrolysis applications.     

Electrodeposition of Mo-doped NiFex nanospheres on 3D graphene fibers for efficient overall alkaline water splitting

Developing efficient bifunctional catalysts for hydrogen and oxygen evolution reactions (HER/OER) has attracted great interest in hydrogen production from water splitting. In this work, a novel material of Mo-doped NiFe_x nanospheres on 3D graphene fibers (Mo-NiFe_x/3DGFs) has been successfully fabricated through a simple and cheap one-step electrodeposition method. The Mo-NiFe_x/3DGFs possessed ultra-high conductivity and specific surface area, greatly benefiting to electrocatalytic hydrolysis activity. And it was found that Fe element could obviously promote OER process, while Mo doping facilitated both OER and HER reactions. We proved that there existed synergetic roles between Fe and Mo element, which could realize the control of the electronic structure and optimize the adsorption/desorption of intermediates. And electrochemical tests showed that the Mo–Ni/3DGFs exhibited a relatively smaller overpotential of 109.9 mV for HER, while the Mo-NiFe_x/3DGFs presented better OER performance with an overpotential of 240.8 mV at the current density of 100 mA cm^-2 in 1.0 M KOH. Finally, a system for overall water splitting constructed by Mo–Ni/3DGFs||Mo–NiFe_0.68/3DGFs electrodes has a low cell voltage of 1.52 V at 10 mA cm^?2 and long-term stability, exceeding most of literature results. Our findings provide insight into possibilities for the simple synthesis of high-performance and cheap catalysts, and laid the foundation for the practical application of transition metal catalysts.     

Modulating interfacial charge redistribution of Ni2P/CuCo2S4 p-n nano-heterojunctions for efficient electrocatalytic overall water splitting

Fabricating effective yet inexpensive catalysts is an important target in the research of water electrolysis and clean energy generation. Key challenges still remaining in this area are the rich density of surface-active sites, efficient interfacial charge transfer and improved reaction kinetics. Herein, Ni₂P/CuCo₂S₄ p-n junctions are constructed via an in situ hydrothermal growth of Ni₂P nanoparticles on CuCo₂S₄ nanosheets. Extensive X-ray photoelectron, optical absorption and electrochemical spectroscopy studies coupled with density functional theory calculations provide a mechanistic understanding of the electrochemical behaviour of these catalysts. The integrated Ni₂P/CuCo₂S₄ p-n junctions, owing to the intimate interfacial interactions, offer interesting possibilities to purposively modulate the electronic structure of active sites at the interface, and thus to improve the hydrogen adsorption energetics and electrochemical reaction kinetics. As a result, the catalyst with 30 wt% Ni₂P content displays high intrinsic electrocatalytic activity, requiring overpotentials of 183 and 360 mV to deliver 10 mA cm⁻² for HER and 40 mA cm⁻² for OER in alkaline media, respectively, far lower than those of individual Ni₂P (400 and 520 mV) and CuCo₂S₄ (348 and 380 mV), further showing remarkable durability for 30 h. In addition, an alkaline two-electrode water electrolyzer assembled by Ni₂P/CuCo₂S₄ nano-heterojunctions exhibits a relatively low cell potential of 1.67 V at 10 mA cm⁻². These Ni₂P-modified CuCo₂S₄ heterostructures demonstrate great potential for renewable hydrogen production technologies, including water electrolysis.     

Efficient bifunctional hydrogen and oxygen evolution reaction electrocatalyst based on the NU-1000/CuCo2S4 heterojunction

One of the current necessities to produce clean energy is the logical design of inexpensive noble-metal free electrocatalysts with developed structure and composition for electrochemical water splitting. In this study, we introduce a new core-shell-structured bifunctional electrocatalyst of NU-1000/CuCo₂S₄ for oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and overall water splitting for the first time. Own to unique structure with rich porosity, high electrical conductivity, high stability and larger density of active sites, this nanocomposite can produce water electrolysis in a 1 M KOH solution. The electrochemical measurements show overpotentials of 335 mV for OER and 93 mV for HER at a current density of 10 mAcm⁻². Also, the NU-1000/CuCo₂S₄ nanocomposite exhibits Tafel slope values of 110 mV dec⁻¹ and 103 mV dec⁻¹ for HER and OER, respectively. Besides, NU-1000/CuCo₂S₄ presents a significant long-term stability in a 72 h run. Additionally, NU-1000/CuCo₂S₄ requires 1.55 V to deliver 10 mA cm⁻² current density in overall water splitting. According to these results, we hope to use this electrocatalyst in producing oxygen and hydrogen from water.     

Amorphous-crystalline cobalt-molybdenum bimetallic phosphide heterostructured nanosheets as Janus electrocatalyst for efficient water splitting

Efficient and sustainable Janus catalysts toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are highly desirable for future hydrogen production via water electrolysis. Herein we report an active Janus electrocatalyst of amorphous-crystalline cobalt-molybdenum bimetallic phosphide heterostructured nanosheets on nickel foam (CoMoP/CoP/NF) for efficient electrolysis of alkaline water. As-reported CoMoP/CoP/NF consists of amorphous bimetal phosphide nanosheets doped with crystalline CoMoP/CoP heterostructured nanoparticles on NF. It can efficiently catalyze both HER (η = 127 mV@100 mA cm^?2) and OER (η = 308 mV@100 mA cm^?2) in alkaline electrolyte with long-term durability. Serving as anode and cathode of water electrolyzer, CoMoP/CoP/NF generates electrolytic current of 10, 50 and 100 mA cm^?2 at low voltage of 1.50, 1.59, and 1.67 V, respectively.     

Self-supported hierarchical porous FeNiCo-based amorphous alloys as high-efficiency bifunctional electrocatalysts toward overall water splitting

Rationally designing an efficient and cost-effective bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a primary matter in applying electrocatalytic water splitting. Herein, a self-supported FeNiCo-based amorphous catalyst with a hierarchical micro/nanoporous structure is fabricated by dealloying an amorphous/nanocrystalline precursor. The amorphous nanoporous framework enables the prepared electrocatalyst to afford fast reaction kinetics, abundant active sites, and enhanced electrochemical active surface areas (ECSAs). Such structural advantages and the synergistic effects of the ternary transition metals contribute to a dramatic catalytic activity of this electrocatalyst under alkaline conditions, which delivers the current density of 10 mA cm⁻² at a low overpotential of 134 mV for HER and 206 mV for OER, respectively. Furthermore, a full electrolysis apparatus constructed by the self-supported hierarchical micro/nanoporous FeNiCo-based amorphous electrocatalyst as both cathode and anode acquires a dramatically low voltage of 1.58 V operating at 10 mA cm⁻² along with stability for more than 24 h for overall water splitting.