A completely slot die coated membrane electrode assembly

This work shows how to manufacture completely coated membrane electrode assemblies (CC-MEAs) for PEM water electrolysis by only using a slot die. Platinum, Nafion^®, and IrO₂ dispersions are successively coated to the respective dried layer. For comparison reasons, MEAs with the same Iridium loading of 2.1 mg cm⁻² and Platinum loading of 0.4 mg cm⁻², assembled with a commercial membrane of the same 20 μm thickness, were produced via decal method. Differences in polarization curves are attributed to the lower high frequency resistance of CC-MEAs determined by impedance spectroscopy. The easy-to-scale CC-MEA method presented here offers the advantages of direct membrane deposition (DMD) without the challenge of homogenously coating a porous transport layer (PTL). Therefore, it allows a free choice of different PTLs – regardless if in sintered form or as expanded metal. The comparability between the produced CC-MEAs and published DMD results is shown by means of cross-sectional and electrochemical measurements.     

Two-dimensional multi-physics modeling of porous transport layer in polymer electrolyte membrane electrolyzer for water splitting

Polymer electrolyte membrane (PEM) electrolyzers have received increasing attention for renewable hydrogen production through water splitting. In present work, a two-dimensional (2-D) multi-physics model is established for PEM electrolyzer to describe the two-phase flow, electron/proton transfer, mass transport, and water electrolysis kinetics with focus on the porous transport layer (PTL) and the channel-land structure. After comparing four sets of experimental data, the model is employed to investigate PTL thickness impact on liquid water saturation and local current density. It is found that the PTL under the land may have much lower liquid saturation than that under the channel due to land blockage. The PTL thickness may significantly impact liquid water access to the catalyst layer (CL) under the land. Specifically, the 100 μm thick PTL shows less than 1% liquid saturation at the CL-PTL interface under 4–5 A/cm², leading to water starvation and electrolyzer voltage increase. As the operating current density decreases under 2–3.5 A/cm², the liquid saturation recovers and increases to about 10–20%. In thicker PTLs, the liquid saturation is higher under the land reaching 30–40% at the CL-PTL interface under 5 A/cm² for 200 and 500 μm thick PTLs. For the 100 μm thick PTL, the local current density drops to below 0.5 A/cm² under the land with 5 A/cm² average current density. For the 200 and 500 μm thick PTLs, the local current is almost uniform in the in-plane direction. The numerical model is extremely valuable to investigate PTL properties and dimensions to optimize channel-land design and configuration for high performing electrolyzers.     

Experimental validation of the “EasyTest Cell” operational principle for autonomous MEA characterization

The paper presents the experimental validation of the “EasyTest Cell” operational principle via comparative electrochemical tests on MEAs carried out in three types of electrochemical hydrogen energy conversion (EHEC) testing cells: conventional polymer electrolyte membrane fuel cells (PEMFC) and polymer electrolyte membrane water electrolyzers (PEMWE), properly equipped with all the required auxiliaries (products conditioning and supplying, reagents removal, etc.), and the simple, autonomous EasyTest Cell. Along with EasyTest Cell validation and demonstration of its advantages, the influence of argon pressure during sputtering on the electrode characteristics, including gas diffusion limitations was investigated. The electrodes under investigation were magnetron sputtered C/Ti/IrO_x (IrO_x loading in the range 0.12–0.4 mg cm⁻²), C/Ti/IrO_x/Pt/IrO_x (IrO_x 0.08/Pt 0.06/IrO_x 0.08 mg cm⁻²), sputtered at various argon pressure C/Ti/Pt (0.15 and 0.25 mg cm⁻²), and commercial ELAT electrode (V.21, Lot # MB030105-1, Pt loading 0.5 mg cm⁻², E-TEK). The results obtained proved the reliability, simplicity (running-periphery-free) and broadened experimental possibilities of EasyTest Cell over PEMFC and PEMWE single cell testing. Thus, significant cost reduction and resource saving in R&D laboratory can be achieved. Moreover, validation of EasyTest Cell contributes not only to testing facilitations, but potentially to standardization of MEA testing since it gives possibilities for precise control and more uniform distribution of the working parameters applied to the testing object, which are both compulsory for performance comparison and qualifying.     

Promoted electrocatalytic hydrogen evolution performance by constructing Ni12P5–Ni2P heterointerfaces

Transition metal phosphides (TMPs) have been considered as cheap alternatives of precious metal platinum for electrochemical hydrogen evolution reaction (HER). In the past decades, many reports have indicated that the engineering of heterointerfaces between different components could efficiently enhance the activity of HER catalysts. Here, we report a facile method to construct Ni₁₂P₅–Ni₂P heterostructure by using a low temperature phosphorization strategy. The obtained Ni₁₂P₅–Ni₂P heterostructure shows high activity toward HER with an overpotential value of 166 mV at 10 mA cm^?2 and a Tafel slope of 60 mV dec^?1 in 0.5 M H₂SO₄. Compared with pure Ni₂P and Ni₁₂P₅, the Ni₁₂P₅–Ni₂P heterostructure has more active sites and faster HER kinetics due to the presence of the interfaces between Ni₁₂P₅ and Ni₂P. Furthermore, we used the obtained Ni₁₂P₅–Ni₂P as cathodic catalyst and IrO₂/Ti as anodic material to set up a proton exchange membrane (PEM) electrolyzer which shows good stability after 120 h continuous constant current electrolysis at 200 mA cm^?2. This work demonstrates the positive effect of heterostructure for HER catalysts and provides a feasible strategy for constructing earth-abundant electrocatalysts.     

Synthesis and electrochemical properties of nano-composite IrO2/TiO2 anode catalyst for SPE electrolysis cell

A composite catalyst of nano-grade IrO₂/TiO₂ powder is synthesized by Adams’ fusion method for reducing overvoltage of solid polymer electrolyte (SPE) cell and cost-down of noble metal catalyst, simultaneously. The IrO₂/TiO₂ catalysts, which has a porous composite nanostructure, are prepared according to molar ratio of Ir and Ti element with a specific surface area of 34.1–55.3 m² g^?1. It is found that crystal structure of TiO₂ is more dominated by the rutile phase than by Anatase. For a SPE system, total catalyst loading of anode which made of TiO₂ and IrO₂ is prepared as low as 0.77 mg cm^?2 or less, in which the loading amount of the IrO₂ only is set to 0.6 mg cm^?2 or less. The anode catalyst layer of about 10 ? thickness is coated on the membrane (Nafion 212) for the membrane electrode assembly (MEA) by the decal method. The strong adhesion between the catalyst electrode the membrane is observed by Scanning electron microscopy (SEM). Linear sweep voltammetry (LSV) results shows that the nano-composite IrO₂/TiO₂ catalysts has better oxygen evolution reaction (OER) than that of the synthesis IrO₂ only. Finally, the IrO₂/TiO₂ catalysts is applied as anode electrode for SPE cells and it is observed that in spite of the lower loading amount of the IrO₂ less than 0.5 mg cm^?2, working voltage of 1.68 V is observed at a current density of 1 A cm^?2 and operating temperature of 80 °C.     

Investigation of IrO2 electrocatalysts prepared by a sulfite-couplex route for the O2 evolution reaction in solid polymer electrolyte water electrolyzers

IrO₂ electrocatalysts were prepared and electrochemically characterized for the oxygen evolution reaction in a Solid Polymer Electrolyte (SPE) electrolyzer. By using a sulfite complex-based preparation procedure, an amorphous iridium oxide precursor was obtained at 80 °C, which was, successively, calcined at different temperatures: 350 °C, 400 °C and 450 °C. A physico-chemical characterization was carried out by X Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray-photoelectron spectroscopy (XPS). The various IrO₂ catalysts were sprayed onto a Nafion 115 membrane with a loading of 2.5 mg cm⁻² to form the anode. A Pt/C catalyst (Pt loading 0.5 mg cm⁻²) was used as cathode. The best electrochemical performance was obtained for the cell based on the IrO₂ calcined at 350 °C. The maximum current density at high potentials (1.8  V) was about 1.75 A cm⁻². Accelerated time-tests at 2 A cm⁻² demonstrated a suitable stability of the IrO₂ calcined at 350 °C; however, the intrinsic stability appeared to increase with the calcination temperature. The sample calcined at 400 °C could represent a good compromise between performance and intrinsic stability.     

(IrOx – Pt)/Ti bifunctional electrodes for oxygen evolution and reduction

Mixed Ir–Pt electrocatalytic films on Ti metal supports were prepared via a galvanic deposition process. Two types of (Ir – Pt)/Ti electrodes were prepared with different Ir–Pt compositions (Ir/Pt atomic composition ratios of 1.74 and 0.44, based on ICP-MS measurements) and of a similar total metal loading (0.15 and 0.12 mg cm^?2). The simultaneous deposition of both metallic Ir and Pt occurred spontaneously upon immersion of a freshly etched Ti metal substrate into a composite solution of Ir(IV) and Pt(IV) complexes of variable concentration. This was followed by electrochemical anodization to convert Ir to IrO_x. Both electrodes showed homogeneous Ir and Pt dispersion on the Ti surface. The bifunctional electrocatalytic performance of (IrO_x/Ir – Pt)/Ti electrodes has been tested towards the oxygen evolution (OER) and reduction (ORR) reactions in acidic solutions. The thus prepared Ti-supported Ir–Pt film electrodes exhibited satisfactory performance towards both reactions, with mass-specific currents for OER being higher than those at a single component IrOx/Ir/Ti electrode and the ones for ORR being comparable to those at a single component Pt/Ti electrode.     

SO2-depolarized electrolysis using porous graphite felt as diffusion layer in proton exchange membrane electrolyzer

The hybrid sulfur (HyS) process, which is composed of SO₂-depolarized electrolysis (SDE) reaction and sulfuric decomposition reaction, is one of the simplest thermochemical cycles for producing hydrogen by water splitting. SDE is currently conducted in a proton exchange membrane (PEM) electrolyzer. In this work, a novel PEM electrolyzer structure is proposed. Graphite felt with large void content is used as the diffusion layer. In the electrolyzer, porous graphite felt plays the role of evenly distributing fluid and conducting electricity. The gap between the polar plate and the catalytic layer is occupied by the electrolyte solution and graphite felt, which effectively reduces the ohmic impedance of the electrolyzer. The effects of the main parameters including graphite felt compression ratio, anodic fluid flow rate, and sulfuric acid concentration, as well as temperature are investigated. Under optimized operating conditions, the current density reaches 800 mA/cm² at cell voltage of 1.094 V, which is remarkably better than reported SDE performance using conventional PEM electrolyzers.     

Membrane electrode assemblies with low noble metal loadings for hydrogen production from solid polymer electrolyte water electrolysis

High performance membrane electrode assemblies (MEAs) with low noble metal loadings (NMLs) were developed for solid polymer electrolyte (SPE) water electrolysis. The electrochemical and physical characterization of the MEAs was performed by I–V curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Even though the total NML was lowered to 0.38 mg cm⁻², it still reached a high performance of 1.633 V at 2 A cm⁻² and 80 °C, with IrO₂ as anode catalyst. The influences of the ionomer content in the anode catalyst layer (CL) and the cell temperature were investigated with the purpose of optimizing the performance. SEM and EIS measurements revealed that the MEA with low NML has very thin porous cathode and anode CLs that get intimate contact with the electrolyte membrane, which makes a reduced mass transport limitation and lower ohmic resistance of the MEA. A short-term water electrolysis operation at 1 A cm⁻² showed that the MEA has good stability: the cell voltage maintained at ∼1.60 V without distinct degradation after 122 h operation at 80 °C and atmospheric pressure.     

Performance of a PEM water electrolyser using a TaC-supported iridium oxide electrocatalyst

Polymer electrolyte membrane (PEM) water electrolysis is an attractive way of producing carbon-free hydrogen. One of the drawbacks of this method is the need for precious metal-based electrocatalysts. This calls for a highly efficient utilization of the precious metal, which can be obtained by dispersing the precious metal compound onto a catalyst support. Electrocatalysts with 50, 70 and 90 wt.% of IrO₂ on a TaC support were tested in a laboratory PEM water electrolyser and compared with pure IrO₂. The temperature was set at 90, 110, 120 and 130 °C respectively and the cell voltage was varied between 1.4 and 1.8 V. The load characteristics and electrochemical impedance spectra were obtained and compared for a range of electrocatalysts. The highest current densities and the lowest charge transfer and cell resistances were found for the 70 wt.% IrO₂ electrocatalyst. By contrast, the pure IrO₂ electrocatalyst showed the lowest current densities and the highest charge transfer and cell resistance. For example, the relative difference in current densities between the 70 wt.% IrO₂ and the pure IrO₂ electrocatalyst attained 36% at 130 °C and 1.7 V. All of the supported electrocatalysts showed a higher efficiency of utilization of the precious metal than the pure IrO₂.     

RuO2 supported on Sb-doped SnO2 nanoparticles for polymer electrolyte membrane water electrolysers

With a colloid method, RuO₂ was deposited on Sb-doped SnO₂ nanoparticles (ATO, Aldrich, 30-40 nm), which was employed as a novel support material for anode catalysts of polymer electrolyte membrane water electrolysers (PEMWE). Distinctive RuO₂ nanoparticles (10-15 nm) were stably deposited on ATO nanoparticles, which were characterized with XRD and SEM. RuO₂/ATO exhibited higher activity than unsupported RuO₂ for oxygen evolution. A PEMWE single cell with 10 mg cm⁻² 20 wt.% RuO₂/ATO achieved 1.56 V at 1 A cm⁻² at 80 °C.     

Novel (Ir,Sn,Nb)O2 anode electrocatalysts with reduced noble metal content for PEM based water electrolysis

A solid solution of IrO₂, SnO₂ and NbO₂, denoted as (Ir,Sn,Nb)O₂, of compositions (Ir_1−2xSn_xNb_x)O₂ with x = 0, 0.125, 0.20, 0.25, 0.30, 0.35, 0.40, 0.425 and 0.50 has been synthesized by thermal decomposition of a homogeneous mixture of IrCl₄, SnCl₂·2H₂O and NbCl₅ ethanol solution coated on pretreated Ti foil. The (Ir,Sn,Nb)O₂ thin film of different compositions coated on Ti foil has been studied as a promising oxygen reduction anode electrocatalyst for PEM based water electrolysis. It has been identified that (Ir,Sn,Nb)O₂ of composition up to x = 0.30 [(Ir_0.40Sn_0.30Nb_0.30)O₂] shows similar electrochemical activity compared to pure IrO₂ (x = 0) resulting in ∼60 mol.% reduction in noble metal content. On the other hand, (Ir,Sn,Nb)O₂ of composition x = 0.20 [(Ir_0.20Sn_0.40Nb_0.40)O₂] shows only 20% lower activity compared to pure IrO₂ though the noble metal oxide, IrO₂ loading is reduced by 80 mol.%. The accelerated life test of the anode electrocatalyst for 48 h followed by elemental analysis of the electrolyte shows that (Ir,Sn,Nb)O₂ improves the stability of the electrode in comparison to pure IrO₂ electrocatalyst in oxygen reduction processes. The excellent electrochemical activity as well as long term structural stability of (Ir,Sn,Nb)O₂ during water electrolysis has been discussed using first-principles calculations of the total energies, electronic structures, and cohesive energies of the model systems.     

Quantifying potential losses of non-Pt MEAs for gas-phase HBr PEM electrolyzer to produce hydrogen

Gas-phase HBr can be converted to hydrogen and bromine in a proton exchange membrane (PEM) electrolyzer. However, due to high cost and the poisoning of bromine and bromide ions on Pt electrodes, non-Pt MEAs (membrane electrode assembly) need to be developed and evaluated. In this paper, RuO₂, carbon (Vulcan XC 72R) and TiO₂–Nb (10% wt.) are prepared as anodes, and IrO₂/C and MoS₂ are prepared as cathodes for incorporation into MEAs. The individual electrodes in these MEAs are then evaluated by de-convoluting the individual voltage losses in-situ from the total electrolyzer voltage. On the anode, Pt, Vulcan XC 72R, TiO₂–Nb (10% wt.) and RuO₂ are all found to have comparable activity toward bromine evolution. On the cathode, Pt was more active toward the hydrogen evolution reaction (HER) compared to IrO₂/C, and both were far superior to MoS₂.     

Microwave-assisted facile synthesis of cobaltiron oxide nanocomposites for oxygen production using alkaline anion exchange membrane water electrolysis

In this study, a rapid, scalable, and cost-effective method was developed for synthesizing cobalt–iron metal oxide catalysts for water electrolysis. Cobalt-iron metal oxide catalysts were synthesized using the microwave-assisted hydrothermal methods by varying the molar ratios of cobalt and iron. When the cobalt to iron ratio was 2:1, its electrolytic cell yielded the onset potential of only 1.56 V at 10 mA cm⁻², which is close to the thermodynamically reversible potential. When its cell potential was at 1.8 V, the cell current density was approximately 130 mA cm⁻². The results of the stability test showed a steady-state cell current density of 130 mA cm⁻² and remained constant for more than 16 h at a continuous cell potential of 1.8 V. Compared with other catalysts, cobalt–iron metal oxide catalysts showed lower overpotential and lower Tafel slope than did conventional precious metal catalysts such as PtO₂ and IrO₂. Cobalt-iron metal oxide catalysts serve as an inexpensive route to large-scale commercialization through facile synthesis for enhanced electrochemical water splitting.     

Characterisation tools development for PEM electrolysers

Electrochemical impedance spectroscopy (EIS), current interrupt (CI) and current mapping (CM) were investigated as in-situ characterisation tools for PEM electrolysers. A 25 cm² cell with titanium anode and carbon cathode plates were utilised in this study. A commercial MEA consisting of 1 mg IrO₂/cm² on the anode and 0.3 mg Pt/cm² on the cathode was used. The electrocatalyst was deposited on Nafion^® membranes. The electrochemical losses in a PEM electrolyser namely: activation, ohmic and mass transfer losses were identified using EIS and CI and both the advantages and disadvantages of the methods were discussed. The current distribution over the membrane electrode assembly (MEA) at different current densities was measured using the current mapping method. It is also shown that under the given experimental conditions the current density decreases along the serpentine flow field.     

Crystallization behavior-dependent electrocatalytic activity and stability of Ti/IrO2RuO2SiO2 anodes for oxygen evolution reaction

IrO₂RuO₂SiO₂ ternary oxide coatings were fabricated on Ti substrate using a sol-gel route. The impacts of calcination conditions (e.g., temperature and time) on the electrocatalytic activity and stability of the anodes were explored. It was found that the calcination temperature and time significantly impact the electrocatalytic properties of the anode for the oxygen evolution reaction (OER). This can result from the properties of the surface (e.g., defects, crystallinity and crystallite size) as well as the preferred orientation of the active components. The amount of the defects of the coatings decreases with the increase of the calcination temperature and time. Besides, the crystallinity and crystallite size increase with the increase of calcination temperature and time. The amorphous oxide coating can be observed from the sample calcined at 350 °C for 15 min, while this coating can be crystallized when the calcination time is 60 min. The coatings calcined in the temperature range between 350 and 450 °C show preferred (101) planes of IrO₂ and RuO₂ crystallites, whereas the coatings calcined at the temperatures higher than 450 °C show the (211) orientation. The increase of calcination time does not change the preferred orientation of IrO₂ and RuO₂. The calculated voltammetric charges suggest that the active surface area of the prepared coating is dominated by the “outer” active surface area over the entire calcination temperature and time ranges. Given the electrocatalytic activity and stability of all investigated anodes, the anode calcined at 450 °C for 15 min is considered the most suitable for applications.     

IrRuOx/TiO2 a stable electrocatalyst for the oxygen evolution reaction in acidic media

Proton Exchange Membrane Electrolysis of Water (PEMWE) stands out as a scalable, CO₂-free process to produce H₂ for energy delivery and industrial applications. Due to the limited Ir and Ru worldwide availability, one of the main challenges for the GW-scale PEMWE implementation is the loading reduction of these metals in the anodic catalytic layer. Here, Ir–Ru loading (5 wt%Ir-40 wt%Ru) was deposited through their impregnation over TiO₂, followed by a thermal-oxidative treatment, obtaining IrRuO_x/TiO₂ catalyst. SEM-EDS and HR-TEM confirmed the homogeneous dispersion of IrRuO_x on TiO₂. The supported catalyst showed a 1.4-fold higher mass activity (85 mA/mg Ir–Ru) for the oxygen evolution reaction (OER) than a mechanical mixture of IrO₂–RuO₂ 1:3 (54 mA/mg_Ir+Ru) in H₂SO₄ 0.5 M, at 1.52 V/RHE. Furthermore, the supported catalyst retains 90% of its catalytic activity after 100 reaction cycles suggesting the RuO₂ intermediate species stabilization by IrO_x, which can avoid its irreversibly transform into hydrous RuO_x.     

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.     

Activity and stability optimization of RuxIr1-xO2 nanocatalyst for the oxygen evolution reaction by tuning the synthetic process

IrO₂ and RuO₂ are known as two of the best catalysts for the oxygen evolution reaction (OER) in acidic electrolyte. It is reported that RuO₂ has higher OER catalytic activity, while IrO₂ possesses better electrochemical stability during the OER process in acid. Therefore, many combined strategies have been proposed to utilize the advantages of both IrO₂ and RuO₂ catalysts in water electrolysis applications. In this article we describe how, by tuning the wet-chemical synthesis process in which the Ir precursor is added after the synthesis of RuO₂ nanoparticles (NPs) (two-step), the Ru_0.5Ir_0.5O₂ NPs have been synthesized to improve the OER catalytic activity in both acidic and alkaline media. In detail, the specific OER activity of the Ru_0.5Ir_0.5O₂ NPs (with a particle size of ca. 10 nm) is 48.9 μA cm⁻² at an overpotential ŋ = 0.22 V (vs. RHE) and 21.7 μA cm⁻² at ŋ = 0.27 V (vs. RHE) in 0.1 M HClO₄ and 0.1 M KOH, respectively. These values are higher than those for the one-step (Ir_0.5+Ru_0.5)O₂ NPs (obtained by contemporaneously adding both Ru and Ir precursors), which are 19.5 and 15.5 μA cm⁻² at the same measuring conditions, respectively. Additionally, with more IrO₂ component distributed on the particle surface, the two-step Ru_0.5Ir_0.5O₂ NPs show better OER catalytic stability than RuO₂ NPs.     

Low Ir-content Ir/Fe@NCNT bifunctional catalyst for efficient water splitting

In order to reduce the cost of electrocatalysts and increase the exposure of the Ir active sites while ensuring the stability of the catalyst, a N-doped carbon nanotube (NCNT) is applied as a conductive support to confine the Ir clusters for avoiding them growing up via a modified method based on pyrolysis of a mixture of melamine, ferric chloride and iridium trichloride. It is found that Ir species in the as-obtained Ir(20)/Fe@NCNT-900 composite exist in two forms, Ir nanoclusters (1–2 nm) dotted on the wall of NCNT and the Ir atomically scattered on the Fe nanoparticles wrapped in the NCNT. Although the Ir content of Ir(20)/Fe@NCNT-900 is extremely low (～4 wt% Ir), the composite catalyst delivers excellent activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with an exceptionally low overpotential of 4.7 mV/11 mV for HER and 300 mV/270 mV for OER to drive 10 mA cm^?2 in 0.5 M H₂SO₄/1.0 M KOH electrolyte respectively, which exceeds the commercial Pt/C (20 wt% Pt) and IrO₂ benchmarks. In addition, it has much higher mass activity for OER at 1.55 V (1.78 A mg^?1_Ir) than those of the referenced catalysts in acid. The cell voltage of the two-electrode system assembled by Ir(20)/Fe@NCNT-900 for total water splitting in acidic and alkaline media are only 1.520 V and 1.510 V to afford 10 mA cm^?2 separately, lower than that of Pt/C||IrO₂ and with a good stability. Our work provides a construction method of low-content precious metal composite catalysts which can be applied in OER and overall water splitting field.