Improving the water electrolysis performance by manipulating the generated nano/micro-bubbles using surfactants

The impeded mass transfer rate by on-site-generated gas bubbles at both cathode and anode dramatically reduces the energy conversion efficiency of the proton exchange membrane water electrolyzer(PEMWE).Herein,we report a surfactant-assistant method to accelerate the nano/micro-bubble detachment and the mass transfer rate by reducing the surface tension,resulting in an increase in overall efficiency.Four kinds of surfactants are studied in this work.Only potassium perfluorobutyl sulfonate(PPFBS),which has the structural similarity to Nafion,shows a significant promotion of activity and stability for both hygrogen evolution reaction(HER)and oxygen evolution reaction(OER)in the acidic medium at the high current density region.The HER overpotential at 0.1 A·cm−2 decreased 22%,and the current density at−0.4 V increased 31%by adding PPFBS.The promotion of overall efficiency by PPFBS on a homemade PEMWE was also proven.The reduced surface tension and electrostatic repulsion were the probable origins of the accelerated bubble detachment.

Interfacial engineering of atomic platinum-doped molybdenum carbide quantum dots for high-rate and stable hydrogen evolution reaction in proton exchange membrane water electrolysis

Platinum(Pt)-based electrocatalysts remain the only practical cathode catalysts for proton exchange membrane water electrolysis(PEMWE),due to their excellent catalytic activity for acidic hydrogen evolution reaction(HER),but are greatly limited by their low reserves and high cost.Here,we report an interfacial engineering strategy to obtain a promising low-Pt loading catalyst with atomically Pt-doped molybdenum carbide quantum dots decorated on conductive porous carbon(Pt-MoCx@C)for high-rate and stable HER in PEMWE.Benefiting from the strong interfacial interaction between Pt atoms and the ultra-small MoCx quantum dots substrate,the Pt-MoCx catalyst exhibits a high mass activity of 8.00 A·mgPt−1,5.6 times higher than that of commercial 20 wt.%Pt/C catalyst.Moreover,the strong interfacial coupling of Pt and MoCx substrate greatly improves the HER stability of the Pt-MoCx catalyst.Density functional theory studies further confirm the strong metal-support interaction on Pt-MoCx,the critical role of MoCx substrate in the stabilization of surface Pt atoms,as well as activation of MoCx substrate by Pt atoms for improving HER durability and activity.The optimized Pt-MoCx@C catalyst demonstrates>2000 h stability under a water-splitting current of 1000 mA·cm^(−2)when applied to the cathode of a PEM water electrolyzer,suggesting the potential for practical applications.

Corrosion Investigation by Scanning Electrochemical Microscopy of AISI 446 and Ti-Coated AISI 446 Ferritic Stainless Steel as Potential Material for Bipolar Plate in PEMWE

The components of proton exchange membrane water electrolysers frequently experience corrosion issues, especially at high anodic polarization, that restrict the use of more affordable alternatives to titanium. Here, we investigate localized corrosion processes of bare and Ti-coated AISI 446 ferritic stainless steel under anodic polarization by scanning electrochemical microscopy (SECM) in sodium sulphate and potassium chloride solutions. SECM approach curves and area scans measured at open-circuit potential (OCP) of the samples in the feedback mode using a redox mediator evidence a negative feedback effect caused by the surface passive film. For the anodic polarization of the sample, the substrate generation-tip collection mode enables to observe local generation of iron (II) ions, as well as formation of molecular oxygen. For the uncoated AISI 446 sample, localized corrosion is detected in sodium sulphate solution simultaneously with oxygen formation at anodic potentials of 1.0 V vs. Ag/AgCl, whereas significant pitting corrosion is observed even at 0.2 V vs. Ag/AgCl in potassium chloride solution. The Ti-coated AISI 446 sample reveals enhanced corrosion resistance in both test solutions, without any evidence of iron (II) ions generation at anodic potentials of 1.2 V vs. Ag/AgCl, where only oxygen formation is observed.

Stabilizing high-efficiency iridium single atoms via lattice confinement for acidic oxygen evolution

Stable and efficient single atom catalysts(SACs)are highly desirable yet challenging in catalyzing acidic oxygen evolution reaction(OER).Herein,we report a novel iridium single atom catalyst structure,with atomic Ir doped in tetragonal PdO matrix(IrSAs-PdO)via a lattice-confined strategy.The optimized IrSAs-PdO-0.10 exhibited remarkable OER activity with an overpotential of 277 mV at 10 mA·cm^(-2) and long-term stability of 1000 h in 0.5 M H_(2)SO_(4).Furthermore,the turnover frequency attains 1.6 s^(-1) at an overpotential of 300 mV with a 24-fold increase in the intrinsic activity.The high activity originates from isolated iridium sites with low valence states and decreased Ir–O bonding covalency,and the excellent stability is a result of the effective confinement of iridium sites by Ir–O–Pd motifs.Moreover,we demonstrated for the first time that SACs have great potential in realizing ultralow loading of iridium(as low as microgram per square center meter level)in a practical water electrolyzer.

Modulating metal-organic frameworks for catalyzing acidic oxygen evolution for proton exchangemembrane water electrolysis

Proton exchangemembrane(PEM)water electrolysis represents one of the most promising technologies to achieve green hydrogen production,but currently its practical viability is largely affected by the slow reaction kinetics of the anodic oxygen evolution reaction(OER)in an acidic environment.While noble metal-based catalysts containing iridium or ruthenium are excellent catalysts for the acidic OER,their practical use in PEM electrolyzers is hindered due to their low abundance and high cost.Most recently,metal-organic frameworks(MOFs)have been demonstrated as a perfect platform to facilitate the design of acidic OER catalysts with both high efficiency and cost-effectiveness.Here,we pro-vide a timely and comprehensive overview of the recent progress on MOF-based acidic OER catalysts.The fundamental mechanisms of the acidic OER are first introduced,followed by a summary of the development of pristine MOFs and MOF derivatives as acidic OER catalysts.Importantly,a number of catalyst design strategies are discussed aiming at improving the acidic OER catalytic per-formance of MOF-based candidates.The integration of MOF-based catalysts into real PEM water electrolyzers is also included.Finally,future research directions are provided to achieve better MOF-based catalysts operational in acidic envi-ronments and PEM devices.

Acidic oxygen evolution reaction:Mechanism,catalyst classification,and enhancement strategies

As the most desirable hydrogen production device,the highly efficient acidic proton exchange membrane water electrolyzers(PEMWE)are severely limited by the sluggish kinetics of oxygen evolution reaction(OER)at the anode.Rutile IrO2 is a commercial acid-stable OER catalyst with poor activity and high cost,which has motivated the development of alternatives.However,hitherto most of the designed acidic OER catalysts have disadvantages of low activity or stability,which cannot meet the requirement of industrial applications.Thus,exploring suitable strategies to enhance the activity and stability of cost-effective acidic OER catalysts is crucial for developing the PEMWE technique.In this review,the main OER mechanisms,different types of catalysts,and their activity and stability characteristics are summarized and discussed,and then possible strategies to improve activity and stability are proposed.Finally,the problems and prospects of such catalysts are generalized to shed some light on the future research of advanced catalysts for acidic OER.

Materials Engineering toward Durable Ru-Based Electrocatalysts for Acidic Oxygen Evolution Reaction

Proton exchange membrane water electrolysis(PEMWE)is considered one of the most promising pathways for producing green hydrogen(H2).However,the sluggish kinetic of the anodic oxygen evolution reaction(OER)hinders the overall efficiency of PEMWE.In the past few decades,ruthenium(Ru)-based materials have been developed as highly active and cost-effective OER catalysts while faced with significant durability challenges.To this end,addressing the durability issues of Ru catalysts is imperative for their practical employment in PEMWE.In this review,state-of-the-art advances in understanding the degradation mechanisms of Ru catalysts in acidic conditions are comprehensively discussed.Then,materials engineering strategies to mitigate degradation through the rational design of stable Ru-catalysts are highlighted.Finally,some prospects are provided in terms of exploring the long-term stability of Ru-based catalysts.This review is anticipated to foster a better understanding of Ru-based catalysts in acidic OER and work on novel strategies for the design of stable Ru-based materials.

Ruthenium-lead oxide for acidic oxygen evolution reaction in proton exchange membrane water electrolysis

Developing an active and stable anode catalyst for the proton exchange membrane water electrolyzer(PEM-WE)is a critical objective to enhance the economic viability of green hydrogen technology.However,the expensive iridium-based electrocatalyst remains the sole practical material with industrial-level stability for the acidic oxygen evolution reaction(OER)at the anode.Ruthenium-based catalysts have been proposed as more cost-effective alternatives with improved activity,though their stability requires enhancement.The current urgent goal is to reduce costs and noble metal loading of the OER catalyst while maintaining robust activity and stability.In this study,we design a Ru-based OER catalyst incorporating Pb as a supporting element.This electrocatalyst exhibits an OER overpotential of 201 mV at 10 mA·cm^(-2),simultaneously reducing Ru noble metal loading by~40%.Normalization of the electrochemically active surface area unveils improved intrinsic activity compared to the pristine RuO_(2) catalyst.During a practical stability test in a PEM-WE setup,our developed catalyst sustains stable performance over 300 h without notable degradation,underscoring its potential for future applications as a reliable anodic catalyst.

Supporting IrO_(x) nanosheets on hollow TiO_(2) for highly efficient acidic water splitting

The efficiency of proton exchange membrane water electrolysis(PEM-WE)for hydrogen production is heavily dependent on the noble metal iridium-based catalysts.However,the scarcity of iridium limits the large-scale application of PEM-WE.To address this issue,it is promising to select an appropriate support because it not only enhances the utilization efficiency of noble metals but also improves mass transport under high current.Herein,we supported amorphous IrO_(x) nanosheets onto the hollow TiO_(2) sphere(denoted as IrO_(x)),which demonstrated excellent performance in acidic electrolytic water splitting.Specifically,the annealed IrO_(x)catalyst at 150℃in air exhibited a mass activity of 1347.5 A·gIr^(−1),which is much higher than that of commercial IrO_(2) of 12.33 A·gIr^(−1) at the overpotential of 300 mV for oxygen evolution reaction(OER).Meanwhile,the annealed IrO_(x) exhibited good stability for 600 h operating at 10 mA·cm^(−2).Moreover,when using IrO_(x) and annealed IrO_(x) catalysts for water splitting,a cell voltage as low as 1.485 V can be achieved at 10 mA·cm^(−2).The cell can continuously operate for 200 h with negligible degradation of performance.

Magnetic and electro-catalytic properties of a copper complex with 2-(pyridylmethyl)amino-N,N-bis(2-methylene-4,6-difluorophenol)

A new material for both magnetic coupling and electrocatalytic hydrogen generation based on a copper complex,[（HL）CuCl-CuCl（HL）]HCl 1 is prepared by the reaction of 2-（pyridylmethyl）amino-N,N-bis（2-methylene-4,6-difluorophenol）（H2L） and CuCl2·2H2O.In solid,complex 1 is built from two copper units（[（HL）CuCl]）,and exhibits an antiferromagnetic exchange interaction between copper（Ⅱ） ions（J=-160cm^-1）.In liquid,1 can electrocatalyze hydrogen generation both from acetic acid with a turnover frequency（TOF） of 16.3 moles of hydrogen per mole of catalyst per hour at an overpotential（OP）of 941.6 mV（in DMF）,and a neutral buffer with a TOF of 1415.6 moles of hydrogen per mole of catalyst per hour at an OP of 787.6 mV.