Electrocatalysts For H2 Evolution Research Articles

Directly growth of highly uniform MnS–MoS2 on carbon cloth for advanced H2 evolution electrocatalyst in different pH electrolytes

The activation energy barrier of the H–O bond of water molecules is high, and thus the rate of H2 evolution reaction (HER) via water splitting is very slow. Hence, chemists are committed to finding high-performance, cheap and stable catalysts for realizing efficient H2 production. The molybdenum disulfide (MoS2)-based bimetallic sulfide electrocatalysts are favored by researchers because of their particular structures and properties. Herein, the Waugh type polyoxometalate (POM) is used as raw materials. A series of MnS–MoS2 electrocatalysts are in-situ coupled on carbon cloth (CC) substrate by a hydrothermal sulfidation method. The catalyst MnS-MoS2-CC possesses high catalytic activity for HER in a alkaline electrolyte, showing a low overpotential of 54 mV at a current density of 10 mA cm−2, which is very close to 35 mV of the 20% Pt/C electrode. Meanwhile, under a current density of over 50 mA cm−2, the overpotential of MnS-MoS2-CC is less than that of the 20% Pt/C electrode. Moreover, the electrocatalysts show overpotentials of 141 mV and 201 mV at a current density of 10 mA cm−2 in 0.5 M H2SO4 and 1.0 M phosphate buffer solution (PBS), respectively. Besides the high catalytic activity, the MnS-MoS2-CC electrode shows long-term durability in a wide pH range, which is confirmed by several methods including the tests of linear sweep voltammetry (LSV) curve, current density vs. time (I-t) curve, and scanning electron microscopy (SEM). This work provides a feasible route for the preparation of HER electrocatalysts applied in broad pH conditions, especially for alkaline solutions.

Data-driven design and controllable synthesis of Pt/carbon electrocatalysts for H2 evolution

SummaryTo achieve net-zero emissions, a particular interest has been raised in the electrochemical evolution of H2 by using catalysts. Considering the complexity of designing catalyst, we demonstrate a data-driven strategy to develop optimized catalysts for H2 evolution. This work starts by collecting data of Pt/carbon catalysts, and applying machine learning to reveal the importance of ranking various features. The algorithms reveal that the Pt content and Pt size have the greatest impact on the catalyst overpotentials. Following the data-driven analysis, a space-confined method is used to fabricate the size-controllable Pt nanoclusters that anchor on nitrogen-doped (N-doped) mesoporous carbon nanosheet network. The obtained catalysts use less platinum and exhibit better catalytic activity than current commercial catalysts in alkaline electrolytes. Moreover, the data formed in this work can be used as feedback to further improve the data-driven model, thereby accelerating the development of high-performance catalysts.

Electrolytic Fuel and Oxygen Harvesting from Ultra-Cold, Hypersaline Martian Regolithic Brines

The United States National Aeronautics and Space Administration’s (NASA) current mandate is to land humans on Mars by 2033. The active Maritain water cycle, discovered by NASA’s Phoenix lander and confirmed by other probes, includes a shallow water table, water/ice precipitation and soluble perchlorates in the Martian regolith (soil) which depress water’s freezing point to ca. -60 ⁰C. These conditions enable the concurrent production of hydrogen fuel and life-support oxygen on Mars through perchlorate brine electrolysis. As a solution for astronaut life-support and rocket re-fueling, we demonstrate an in-situ resource utilization (ISRU) approach to produce ultra-pure H2 and O2 from liquid-phase Martian regolithic brine at ca. -36 ⁰C and under Martian atmospheric conditions(1). We built a perchlorate brine electrolyzer utilizing a Pb2Ru2O7-δ pyrochlore O2-evolution electrocatalyst, a Pt/C H2-evolution electrocatalyst and commercial anion exchange membrane separator. Our electrolyzer demonstrated >25x the O2 production rate of the high-temperature, CO2 electrolyzing Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) from NASA’s Mars 2020 mission for the same input power under Martian terrestrial conditions while also avoiding the need to remove CO by-product. This work provides an additional route to help NASA fulfill its mandate to land humans on Mars by 2033. Furthermore, our perchlorate brine electrolyzers are more efficient than state-of-the-art alkaline water electrolyzers on Earth, providing a pathway to utilize sub-optimal input feeds to produce ultra-pure hydrogen and oxygen. References P. Gayen, S. Sankarasubramanian, V. K. Ramani, Fuel and oxygen harvesting from Martian regolithic brine. Proc. Natl. Acad. Sci. U. S. A. 117, 31685–31689 (2020). Figure 1

An [FeFe]‐Hydrogenase Mimic Immobilized through Simple Physiadsorption and Active for Aqueous H2 Production

AbstractMimicking hydrogenases with synthetic complexes is a promising strategy for the design of Earth‐abundant electrocatalysts for H2 evolution as alternative to platinum. Here, we describe a bio‐inspired FeFe electrocatalyst, with a semi‐bridging μ‐CO ligand, active and stable for H2 evolution in acidic aqueous solutions after its physiadsorption onto carbon‐based electrodes.

Fuel and oxygen harvesting from Martian regolithic brine

NASA's current mandate is to land humans on Mars by 2033. Here, we demonstrate an approach to produce ultrapure H2 and O2 from liquid-phase Martian regolithic brine at ∼-36 °C. Utilizing a Pb2Ru2O7-δ pyrochlore O2-evolution electrocatalyst and a Pt/C H2-evolution electrocatalyst, we demonstrate a brine electrolyzer with >25× the O2 production rate of the Mars Oxygen In Situ Resource Utilization Experiment (MOXIE) from NASA's Mars 2020 mission for the same input power under Martian terrestrial conditions. Given the Phoenix lander's observation of an active water cycle on Mars and the extensive presence of perchlorate salts that depress water's freezing point to ∼-60 °C, our approach provides a unique pathway to life-support and fuel production for future human missions to Mars.

Interlayer engineering of molybdenum disulfide toward efficient electrocatalytic hydrogenation

Electrocatalytic hydrogenation (ECH) enables the sustainable production of chemicals under ambient condition; however, suffers from serious competition with hydrogen (H2) evolution and the use of precious metals as electrocatalysts. Herein, molybdenum disulfide is for the first time developed as an efficient and noble-metal-free catalyst for ECH via in situ intercalation of ammonia or alkyl-amine cations. This interlayer engineering regulates phase transition (2H → 1 T), and effectively ameliorates electronic configurations and surface hydrophobicity to promote the ECH of biomass-derived oxygenates, while prohibiting H2 evolution. The optimal one intercalated by dimethylamine (MoS2-DMA) is capable of hydrogenating furfural (FAL) to furfuryl alcohol with high Faradaic efficiency of 86.3%–73.3% and outstanding selectivity of >95.0% at −0.25 to −0.65 V (vs. RHE), outperforming MoS2 and other conventional metals. Such prominent performance stems from the enhanced chemisorption and surface hydrophobicity. The chemisorption of H intermediate and FAL, synchronously strengthened on the edge-sites of MoS2-DMA, accelerates the surface elementary step following Langmuir-Hinshelwood mechanism. Moreover, the improved hydrophobicity benefits FAL affinity to overcome diffusion limitation. Discovering the effective modulation of MoS2 from a typical H2 evolution electrocatalyst to a promising candidate for ECH, this study broadens the scope to exploit catalysts used for electrochemical synthesis.

NiCoP nanoleaves array for electrocatalytic alkaline H2 evolution and overall water splitting

Abstract The development of non-precious, high-efficient and durable electrocatalysts for H2 evolution in alkaline media is highly desirable. Herein we report NiCoP nanoleaves array vertically grown on Ni foam for H2 evolution and overall water splitting via simple hydrothermal treatment and phosphorization. The self-supported NiCoP nanoleaves architecture contributes to more exposed active sites, the smaller contact resistance between catalyst and substrate, faster ion diffusion and electron transfer. As a result, the optimized electrode requires only overpotentials of 98 and 173 mV to achieve current densities of 10 and 100 mA cm−2 in 1.0 M KOH, respectively. Besides, used as both anode and cathode simultaneously, the electrode delivers current densities of 100 and 200 mA cm−2 at cell voltages of only 1.8 and 1.87 V, respectively. Moreover, the relatively high efficiency of about 11.4% for solar-driven water splitting further illustrates the application of our catalyst to sustainable development based on green technologies.

Best Practice for Evaluating Electrocatalysts for Hydrogen Economy.

Screening new electrocatalysts is key to the development of new materials for next-generation energy devices such as fuel cells and electrolyzers. The counter electrodes used in such tests are often made from materials such as Pt and Au, which can dissolve during testing and deposit onto test electrocatalysts, resulting in inaccurate results. The most common strategy for preventing this effect is to separate the counter electrode from the test material using an ion-transporting Nafion membrane. Here, we use X-ray photoelectron spectroscopy, energy-dispersive X-ray analysis, mass spectrometry, and voltammetry to demonstrate the limitations of this approach during constant-current, extended stability testing of electrocatalysts for H2 evolution. We show that Nafion membranes cannot prevent contamination of carbon electrocatalysts by Pt and Au counter electrodes, leading to an apparent increase in the electrocatalytic activity of the carbon. We then demonstrate that carbon counter electrodes in undivided cells can contaminate and deactivate Pt and Au electrocatalysts for H2 evolution. We show that use of a setup composed of a glass frit separating a carbon counter electrode from the test electrocatalyst can prevent these effects. Finally, we discuss these phenomena using H2 evolution at MoS2 and at a K6[P2W18O62](H2O)14/carbon nanotube composite as test reactions.

Cobalt Complex of a Tetraamido Macrocyclic Ligand as a Precursor for Electrocatalytic Hydrogen Evolution

Hydrogen (H2) is a clean fuel that can potentially store renewable energy and overcome some of the environmental problems that arise from fossil-fuel consumption. One attractive approach is to produce H2 from water electrocatalytically using molecular complexes that can be systematically improved through ligand modifications. We report cobalt and nickel complexes supported by tetraamido macrocyclic ligands (TAMLs), which exclusively consist of earth-abundant elements. Although TAML systems are well established in high-valent transition-metal chemistry, little is known about their reactivity in reductive catalysis despite the electron-rich nature of the tetraanionic TAML. Thus we explored the utility of these nucleophilic -ate complexes as potential electrocatalysts for H2 evolution using water as the proton source. Controlled potential electrolysis experiments were performed, and the cobalt TAML variant exhibited catalytic H2 evolution activity in acetonitrile containing 1.0 M water but was inactive in pu...

Closed Bipolar Electrodes for Spatial Separation of H2 and O2 Evolution during Water Electrolysis and the Development of High-Voltage Fuel Cells.

Electrolytic water splitting could potentially provide clean H2 for a future "hydrogen economy". However, as H2 and O2 are produced in close proximity to each other in water electrolyzers, mixing of the gases can occur during electrolysis, with potentially dangerous consequences. Herein, we describe an electrochemical water-splitting cell, in which mixing of the electrogenerated gases is impossible. In our cell, separate H2- and O2-evolving cells are connected electrically by a bipolar electrode in contact with an inexpensive dissolved redox couple (K3Fe(CN)6/K4Fe(CN)6). Electrolytic water splitting occurs in tandem with oxidation/reduction of the K3Fe(CN)6/K4Fe(CN) redox couples in the separate compartments, affording completely spatially separated H2 and O2 evolution. We demonstrate operation of our prototype cell using conventional Pt electrodes for each gas-evolving reaction, as well as using earth-abundant Ni2P electrocatalysts for H2 evolution. Furthermore, we show that our cell can be run in reverse and operate as a H2 fuel cell, releasing the energy stored in the electrogenerated H2 and O2. We also describe how the absence of an ionically conducting electrolyte bridging the H2- and O2-electrode compartments makes it possible to develop H2 fuel cells in which the anode and cathode are at different pH values, thereby increasing the voltage above that of conventional fuel cells. The use of our cell design in electrolyzers could result in dramatically improved safety during operation and the generation of higher-purity H2 than available from conventional electrolysis systems. Our cell could also be readily modified for the electrosynthesis of other chemicals, where mixing of the electrochemical products is undesirable.

New Reactor Designs for Z-Scheme Solar Water Splitting Photocatalysis

Particle suspension reactors for solar water splitting can be an economical alternative to photovoltaic-driven electrolysis. One design resembles Nature’s Z-scheme where two photosystems work in concert to drive overall water splitting. A conceptual Z-scheme reactor has been reported where two compartments on the meter length scale are adjoined side-by-side, each containing photocatalyst particles that drive one half-reaction of overall water splitting, and are connected by a nanoporous material that allows mixing of the liquid electrolyte.1,2 Electronic charge is mediated between the compartments by a dissolved redox shuttle that undergoes oxidation or reduction at the particles. While this design facilitates product separation (i.e. separation of H2 and O2) and therefore circumvents formation of an explosive mixture of gases, active transport of the redox shuttle over these distances has been projected to account for about half of the capital cost of the reactor.1,2 Our team is evaluating the feasibility of new reactor designs where the compartments are stacked vertically. This generates a true tandem light-absorbing reactor where the theoretical maximum solar-to-hydrogen conversion efficiency is ~50% larger than a side-by-side or single light-absorber design. Because the compartments are expected to be ~10 cm tall, this design greatly decreases the distance required for redox shuttle transport therefore reducing or even eliminating the need for forced convection. In my presentation I will report on our team’s progress on this design. We used finite-element numerical methods to model and simulate in two dimensions the transient mass transport processes, light absorption, and electrochemical kinetics in the proposed reactor. The developed model provided insights into the influence of the reactor geometry and operating conditions on the overall performance. The Beer–Bouger–Lambert law was applied to obtain the spatial light-intensity field and volumetric reaction rates were obtained by coupling solid-state photodiode expressions with Butler–Volmer kinetics on the surface of the particles. Model results suggested that a reactor operating at a ~1% solar-to-hydrogen conversion efficiency can operate for greater than half a year without complete loss of redox shuttle at any location in the reactor. Experimentally, we investigated materials over many size scales, from single particles (~10 nm in diameter) to mesoporous thin films (~10 µm thick) to laboratory-scale prototype particle-suspension reactors (on the scale of feet). On the single particle level we used bipolar electrodeposition to create Janus-type particles consisting of model carbon particles with metal and metal-oxide electrocatalysts for H2 evolution and O2 evolution at the poles. We also jammed and covalently bound TiO2 nanoparticles into a single nanopore in a plastic sheet, wetted the particles with liquid electrolyte on both sides, and measured photovoltages that resulted from excitation of few particles. We also synthesized, characterized, and evaluated the photo(electro)chemical performance of BiVO4 and Rh-doped SrTiO3 nanocrystallites as mesoporous thin films and particles in model reactors, and evaluated the transport properties of several redox shuttles. Collectively, our efforts represent strides toward achieving a high-level of techno-economic viability in solar water splitting reactors. Acknowledgments: This work was supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Incubator Program under Award No. DE-EE0006963 and Lawrence Berkeley National Laboratory under Contract No. DE-AC02-05CH11231.

Iron or nickel complexes bearing diphosphine and BIAN ligands as electrocatalysts for H2 evolution

GRAPHICAL ABSTRACT

Beyond Metal-Hydrides: Non-Transition-Metal and Metal-Free Ligand-Centered Electrocatalytic Hydrogen Evolution and Hydrogen Oxidation.

A new pathway for homogeneous electrocatalytic H2 evolution and H2 oxidation has been developed using a redox active thiosemicarbazone and its zinc complex as seminal metal-free and transition-metal-free examples. Diacetyl-bis(N-4-methyl-3-thiosemicarbazone) and zinc diacetyl-bis(N-4-methyl-3-thiosemicarbazide) display the highest reported TOFs of any homogeneous ligand-centered H2 evolution catalyst, 1320 and 1170 s(-1), respectively, while the zinc complex also displays one of the highest reported TOF values for H2 oxidation, 72 s(-1), of any homogeneous catalyst. Catalysis proceeds via ligand-centered proton-transfer and electron-transfer events while avoiding traditional metal-hydride intermediates. The unique mechanism is consistent with electrochemical results and is further supported by density functional theory. The results identify a new direction for the design of electrocatalysts for H2 evolution and H2 oxidation that are not reliant on metal-hydride intermediates.

Toward the rational benchmarking of homogeneous H2-evolving catalysts

Molecular electrocatalysts for H2 evolution are usually studied under various conditions (solvent, proton sources) that prevent direct comparison of their performances. We provide here a rational method for such a benchmark based on (i) the recent analysis of the current-potential response for two-electron-two-step mechanisms and (ii) the derivation of catalytic Tafel plots reflecting the interdependency of turnover frequency and overpotential based on the intrinsic properties of the catalyst, independently of contingent factors such as the cell characteristics. Such a methodology is exemplified on a series of molecular catalysts among the most efficient in recent literature.