Cooperative Boron and Vanadium Doping of Nickel Phosphides for Hydrogen Evolution in Alkaline and Anion Exchange Membrane Water/Seawater Electrolyzers.

Developing low-cost and high-performance transition metal-based electrocatalysts is crucial for realizing sustainable hydrogen evolution reaction (HER) in alkaline media. Here, a cooperative boron and vanadium co-doped nickel phosphide electrode (B, V-Ni2 P) is developed to regulate the intrinsic electronic configuration of Ni2 P and promote HER processes. Experimental and theoretical results reveal that V dopants in B, V-Ni2 P greatly facilitate the dissociation of water, and the synergistic effect of B and V dopants promotes the subsequent desorption of the adsorbed hydrogen intermediates. Benefiting from the cooperativity of both dopants, the B, V-Ni2 P electrocatalyst requires a low overpotential of 148 mV to attain a current density of -100 mA cm-2  with excellent durability. The B, V-Ni2 P is applied as the cathode in both alkaline water electrolyzers (AWEs) and anion exchange membrane water electrolyzers (AEMWEs). Remarkably, the AEMWE delivers a stable performance to achieve 500 and 1000 mA cm-2  current densities at a cell voltage of 1.78 and 1.92 V, respectively. Furthermore, the developed AWEs and AEMWEs also demonstrate excellent performance for overall seawater electrolysis.

Heterostructured V-Doped Ni2 P/Ni12 P5 Electrocatalysts for Hydrogen Evolution in Anion Exchange Membrane Water Electrolyzers.

Regulating the electronic structure and intrinsic activity of catalysts' active sites with optimal hydrogen intermediates adsorption is crucial to enhancing the hydrogen evolution reaction (HER) in alkaline media. Herein, a heterostructured V-doped Ni2 P/Ni12 P5 (V-Ni2 P/Ni12 P5 ) electrocatalyst is  fabricated through a hydrothermal treatment and controllable phosphidation process. In comparison with pure-phase V-Ni2 P, in/ex situ characterizations and theoretical calculations reveal a redistribution of electrons and active sites in V-Ni2 P/Ni12 P5 due to the V doping and heterointerfaces effect. The strong coupling between Ni2 P and Ni12 P5 at the interface leads to an increased electron density at interfacial Ni sites while depleting at P sites, with V-doping further promoting the electron accumulation at Ni sites. This is accompanied by the change of active sites from the anionic P sites to the interfacial Ni-V bridge sites in V-Ni2 P/Ni12 P5 . Benefiting from the interface electronic structure, increased number of active sites, and optimized H-adsorption energy, the V-Ni2 P/Ni12 P5 exhibits an overpotential of 62 mV to deliver 10 mA cm-2 and excellent long-term stability for HER. The V-Ni2 P/Ni12 P5 catalyst is applied for anion exchange membrane water electrolysis to deliver superior performance with a current density of 500 mA cm-2 at a cell voltage of 1.79 V and excellent durability.

Molecular Crowding Electrolytes for Stable Proton Batteries.

Proton electrochemistry is promising for developing post-lithium energy storage devices with high capacity and rate capability. However, some electrode materials are vulnerable because of the co-intercalation of free water molecules in traditional acid electrolytes, resulting in rapid capacity fading. Here, the authors report a molecular crowding electrolyte with the usage of poly(ethylene glycol) (PEG) as a crowding agent, achieving fast and stable electrochemical proton storage and expanded working potential window (3.2 V). Spectroscopic characterisations reveal the formation of hydrogen bonds between water and PEG molecules, which is beneficial for confining the activity of water molecules. Molecular dynamics simulations confirm a significant decrease of free water fraction in the molecular crowding electrolyte. Dynamic structural evolution of the MoO3 anode is studied by in-situ synchrotron X-ray diffraction (XRD), revealing a reversible multi-step naked proton (de)intercalation mechanism. Surficial adsorption of PEG molecules on MoO3 anode works in synergy to alleviate the destructive effect of concurrent water desolvation, thereby achieving enhanced cycling stability. This strategy offers possibilities of practical applications of proton electrochemistry thanks to the low-cost and eco-friendly nature of PEG additives.

Hydrogen-Bond Disrupting Electrolytes for Fast and Stable Proton Batteries.

Rechargeable aqueous proton batteries are promising competitors for the next generation of energy storage systems with the fast diffusion kinetics and wide availability of protons. However, poor cycling stability is a big challenge for proton batteries due to the attachment of water molecules to the electrode surface in acid electrolytes. Here, a hydrogen-bond disrupting electrolyte strategy to boost proton battery stability via simultaneously tuning the hydronium ion solvation sheath in the electrolyte and the electrode interface is reported. By mixing cryoprotectants such as glycerol with acids, hydrogen bonds involving water molecules are disrupted leading to a modified hydronium ion solvation sheaths and minimized water activity. Concomitantly, glycerol absorbs on the electrode surface and acts to protect the electrode surface from water. Fast and stable proton storage with high rate capability and long cycle life is thus achieved, even at temperatures as low as -50 °C. This electrolyte strategy may be universal and is likely to pave the way toward highly stable aqueous energy storage systems.

Electronic Structure Engineering of Single-Atom Ru Sites via Co-N4 Sites for Bifunctional pH-Universal Water Splitting.

The development of bifunctional water-splitting electrocatalysts that are efficient and stable over a wide range of pH is of great significance but challenging. Here, an atomically dispersed Ru/Co dual-sites catalyst is reported anchored on N-doped carbon (Ru/Co-N-C) for outstanding oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in both acidic and alkaline electrolytes. The Ru/Co-N-C catalyst requires the overpotential of only 13 and 23 mV for HER, 232 and 247 mV for OER to deliver a current density of 10 mA cmgeo -2 in 0.5 m H2 SO4 and 1 m KOH, respectively, outperforming benchmark catalysts Pt/C and RuO2 . Theoretical calculations reveal that the introduction of Co-N4 sites into Ru/Co-N-C efficiently modify the electronic structure of Ru by enlarging Ru-O covalency and increasing Ru electron density, which in turn optimize the bonding strength between oxygen/hydrogen intermediate species with Ru sites, thereby enhancing OER and HER performance. Furthermore, the incorporation of Co-N4 sites induces electron redistribution around Ru-N4, thus enhancing corrosion-resistance of Ru/Co-N-C during acid and alkaline electrolysis. The Ru/Co-N-C has been applied in a proton exchange membrane water electrolyzer and steady operation is demonstrated at a high current density of 450 mA cmgeo -2 for 330 h.

Fe-N-C/Fe nanoparticle composite catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells.

Replacing Pt-based catalysts with cost-effective, highly efficient, and durable platinum group metal-free catalysts for the oxygen reduction reaction (ORR) is crucial for commercializing hydrogen fuel cells. Herein, we present a highly active Fe-N-C electrocatalyst that contains both Fe nanoparticles and FeNx active sites derived from an Fe-doped carbonized zeolitic imidazolate framework (ZIF-8). It is found that adjusting the doping amount of Fe in the Fe-doped ZIF-8 precursor alters the morphology of the catalyst after heat treatment. The Fe-N-C-300 composite catalyst with the optimized Fe doping amount exhibits excellent activity, good stability, and remarkable methanol tolerance in the challenging acid environment. This study reveals that a suitable amount of Fe nanoparticles in the catalyst can alter the structure of the FeNx active moieties and increase three-phase boundaries to boost the mass transport, thus leading to improved fuel cell performance. This will have implications for using Fe-N-C catalysts in real applications, as the formation of Fe NPs during the synthesis and reaction is almost inevitable.