Universal Strategy of Bimetal Heterostructures as Superior Bifunctional Catalysts for Electrochemical Water Splitting

Abstract: Exploring highly efficient electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is of great significance for addressing energy and environmental crises. Vacancy engineering has been regarded as a promising way to optimize the catalytic activity of electrocatalysts. Herein, we put forward a conceptually new dual Ni,S vacancy engineering on 2D NiPS3 nanosheet (denoted as V-NiPS3 ) by a simple ball-milling treatment with ultrasonication. This material presents an ideal model for exploring the role of dual vacancies in improving the catalytic activity for overall water splitting. Structural analyses make clear that the formation of dual Ni,S vacancies regulates the electronic structure and catalytic active sites of NiPS3 nanosheet, leading to the superior HER/OER performance. Smaller overpotentials of 124 mV and 290 mV can be achieved at a current density of 10 mA cm-2 for HER and OER, respectively. The OER performance of V-NiPS3 is the best value among all state-of-the-art NiPS3 catalysts. In addition, the assembled two-electrode cell incorporating V-NiPS3 exhibits enhanced catalytic performance with a low cell voltage of 1.60 V at 10 mA cm-2 . This work offers a promising avenue to improve the electrocatalytic performance of the catalysts by engineering dual vacancies for large-scale water splitting.

Abstract: Rational design of non-noble metal electrocatalysts with high intrinsic activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is extremely impressive for sustainable electrocatalytic water splitting systems. However, it still remains a major challenge to engineer bifunctional performance. Here, we put forward a highly efficient water electrolyzer based on Ni3S2-based materials. The hierarchical structure of Ni3S2 can be well regulated for optimizing the HER catalytic activity. The best c-Ni3S2/NF electrode exhibits a much smaller overpotential of 220 mV to reach the current density of 100 mA cm−2. Upon introducing Fe species onto the Ni3S2/NF electrode by a simple dipping/drying method, the intrinsic OER activity can be extremely improved. As a result, the Fe-c-Ni3S2/NF catalyst showed excellent catalytic activity for the OER, including an overpotential of 193 mV at 10 mA cm−2, high specific current density and excellent stability. Post-characterization studies proved that the remaining S anions have an effective influence on improving the OER intrinsic activity. The assembled water electrolyzer also presented superior performance, such as a very low cell voltage of 1.50 V at 10 mA cm−2 and excellent durability for 120 h in alkaline medium. This strategy provides a promising way to design highly active and low-cost materials for overall water electrolysis.

Abstract: Designing low-cost but efficient non-noble-metal bifunctional electrocatalysts is necessary for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the process of water splitting. Herein, we report a self-standing bifunctional electrode by coating MoS2–CoS2 heteronanosheet arrays on porous carbon microtube textile (MoS2–CoS2@PCMT) for alkaline overall water splitting. The abundant MoS2–CoS2 heterogeneous interfaces with electronic interaction (confirmed by X-ray photoelectron spectroscopy) can optimize the adsorption free energies for HER and OER intermediates (supported by the theoretical calculation), making MoS2–CoS2@PCMT achieve lower overpotentials for HER and OER than Pt/C@PCMT and RuO2@PCMT at higher current density. In addition, the freestanding structure of PCMT and the tight adhesion with MoS2–CoS2 heteronanosheets facilitate MoS2–CoS2@PCMT a long-term durability. As a result, the MoS2–CoS2@PCMT||MoS2–CoS2@PCMT couple show a relatively low water-splitting voltage of 1.59 V at 10 mA cm−2, and demonstrate lower cell voltage than the benchmark Pt/C@PCMT||RuO2@PCMT couple at higher current density. This work gives prominence to the design of self-standing electrode structure and coupling of transition metal dichalcogenides to improve the performance of electrocatalysts for water splitting.

Abstract: For practically feasible water splitting to fulfill the need of energy, the development of efficient, robust and long lasting catalyst is necessary. Transition metal compounds facilitates the good catalytic properties due to facile transition of their oxidation states. We here reported a novel process for the synthesis of novel material as cobalt doped iron phosphate thin films. The pristine iron phosphate thin films have synthesized by regular facile hydrothermal method and to achieve doping of the cobalt into iron phosphate, second step hydrothermal ion-exchange process was used. The as synthesized cobalt doped iron phosphate thin film electrode exhibits excellent electrochemical OER and HER catalytic water splitting performance. The prepared material was demonstrated by two electrodes overall water splitting electrolyzer in alkaline medium at lowest potential of 1.72 V to deliver 10 mA/cm2 current density after 4 days’ continuous water splitting test. The outstanding catalytic stability proved 0.4 Co:FePi thin film electrodes are robust water splitting electrocatalyst.

Abstract: The exploration of highly active bifunctional electrocatalysts for acidic electrochemical water splitting has attracted wide attention due to their importance in polymer electrolyte membrane (PEM) electrolyzers. However, existing catalysts normally suffer from low catalytic efficiency under acidic conditions. Herein, we developed a series of Ir-doped CoP nanowires arrays on carbon cloth (Ir-CoP/CC) materials, realizing prominently improved bifunctional catalytic activity for overall water splitting in an acidic medium. The optimized Ir4-CoP/CC catalyst exhibits the smallest overpotential of 38 mV and 237 mV to reach 10 mA cm−2 for HER and OER, respectively. Through systematic experimental research, we find the best intrinsic activity belongs to Ir3-CoP/CC catalyst, which presents superior bifunctional performance with the most economical usage of Ir. As a result, the best acidic water splitting electrolyzer displays a very low voltage of 1.50 V at 10 mA cm−2. This work provides a novel strategy to develop highly active bifunctional catalysts for acidic electrochemical water splitting.

Abstract: A co-doped carbon material, methods of making such materials, and electrochemical cells and devices comprising such materials are provided. The co-doped carbon material comprises a mesoporous carbon material doped with nitrogen and phoshporous (NPMC). The present NPMC exhibit catalytic activity for both oxygen reduction reaction and oxygen evolution reaction and may be useful as an electrode in an electrochemical cell and particularly as part of a battery. The present NPMC materials may be used as electrodes in primary zinc-air batteries and in rechargeable zinc-air batteries and many other energy systems.

Abstract: A comparative investigation was performed to examine the intrinsic catalytic activity and durability of carbon supported Ru, Ir, and Pt nanoparticles and corresponding bulk materials for the electrocatalytic oxygen evolution reaction (OER). The electrochemical surface characteristics of nanoparticles and bulk materials were studied by surface-sensitive cyclic voltammetry. Although basically similar voltammetric features were observed for nanoparticles and bulk materials of each metal, some differences were uncovered highlighting the changes in oxidation chemistry. On the basis of the electrochemical results, we demonstrated that Ru nanoparticles show lower passivation potentials compared to bulk Ru material. Ir nanoparticles completely lost their voltammetric metallic features during the voltage cycling, in contrast to the corresponding bulk material. Finally, Pt nanoparticles show an increased oxophilic nature compared to bulk Pt. With regard to the OER performance, the most pronounced effects of nanosca...

Abstract: The ability of renewable resources to provide all of society's energy needs is shown by using the United States as an example. Various renewable systems are presented, and the issues of energy payback, carbon dioxide abatement, and energy storage are addressed. Pathways for renewable hydrogen generation are shown, and the implementation of hydrogen technologies into the energy infrastructure is presented. The question is asked, Should money and energy be spent on carbon dioxide sequestration, or should renewable resources be implemented instead.

Abstract: Elaborate design of highly active and stable catalysts from Earth-abundant elements has great potential to produce materials that can replace the noble-metal-based catalysts commonly used in a range of useful (electro)chemical processes. Here we report, for the first time, a synthetic method that leads to in situ growth of {210} high-index faceted Ni3S2 nanosheet arrays on nickel foam (NF). We show that the resulting material, denoted Ni3S2/NF, can serve as a highly active, binder-free, bifunctional electrocatalyst for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Ni3S2/NF is found to give ∼100% Faradaic yield toward both HER and OER and to show remarkable catalytic stability (for >200 h). Experimental results and theoretical calculations indicate that Ni3S2/NF’s excellent catalytic activity is mainly due to the synergistic catalytic effects produced in it by its nanosheet arrays and exposed {210} high-index facets.

Abstract: We discuss recent developments in nanostructured molybdenum sulfide catalysts for the electrochemical hydrogen evolution reaction. To develop a framework for performing consistent and meaningful comparisons between catalysts, we review standard experimental methodologies for measuring catalyst performance and define two metrics used in this perspective for comparing catalyst activity: the turnover frequency, an intrinsic activity metric, and the total electrode activity, a device-oriented activity metric. We discuss general strategies for synthesizing catalysts with improved activity, namely, increasing the number of electrically accessible active sites or increasing the turnover frequency of each site. Then we consider a number of state-of-the-art molybdenum sulfide catalysts, including crystalline MoS2, amorphous MoSx, and molecular cluster materials, to highlight these strategies in practice. Comparing these catalysts reveals that most of the molybdenum sulfide catalysts have similar active site turnov...