Enhanced OER Performance and Dynamic Transition of Surface Reconstruction in LaNiO3 Thin Films with Nanoparticles Decoration

Evaluating the Effect of Oxygen Vacancies on the Oxygen Evolution Reaction (OER) Activity of LaNiO3

In this work, we have investigated the effect of oxygen vacancies on the surface composition, electronic structure, and oxygen evolution reaction (OER) performance of LaNiO3. The results show that the OER performance of LaNiO3 can be improved both by decreasing the oxygen partial pressure during film growth and annealing the thin film in a H2 atmosphere. X-ray photoemission spectroscopy (XPS) shows a significant increase in the Ni:La ratio on the LaNiO3 surface after the introduction of oxygen defects, especially after H2 treatment, where the Ni:La ratio reaches 3.5:1. The presence of oxygen vacancies leads to the aggregation of Ni on the surface of LaNiO3, which plays a crucial role in enhancing the OER performance of LaNiO3. In addition, the OER activity of both LaNiO3 and oxygen vacancy rich LaNiO3 decreases upon cyclic voltammetry (CV) between 1.0 and 1.5 V versus the RHE with an increase in the cycle number. XPS results reveal that the CV treatments lead to a decrease in the Ni concentration at the LaNiO3 surface, which is an important factor for the decrease in the OER performance of LaNiO3 as well as oxygen vacancy rich LaNiO3.

Bifunctional electrocatalytic performance of MgAlCe-LDH/β-Ni(OH)2/Ni foam in total natural seawater splitting

Electrocatalytic seawater splitting is a potential solution to environmental problems, as seawater is a plentiful supply of hydrogen sources in nature. Hence, the development of bifunctional electrodes exhibiting outstanding performance in both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is essential for the efficacy of total seawater splitting. Herein, we employed a straightforward method for in situ creation of β-Ni(OH)2 on Ni foam, followed by a hydrothermal approach to manufacture MgAlCe-LDH on β-Ni(OH)2/Ni foam. The linear sweep voltammetry (LSV) experiments demonstrate that the MgAlCe-LDH/β-Ni(OH)2/Ni foam exhibits superior performance for both the OER and the HER in a natural seawater electrolyte compared to the MgAlCe-LDH/Ni foam, β-Ni(OH)2/Ni foam, and Ni foam. Consequently, the MgAlCe-LDH/β-Ni(OH)2/Ni foam requires an 80 mV overpotential for OER and 337 mV for HER to attain a current density of 10 mA cm-2. The enhanced electrocatalytic activity of MgAlCe-LDH/β-Ni(OH)2/Ni foam can be attributed to boosting exposed active sites, improving electronic interaction, and increasing charge transfer capacity resulting from the synthesis of MgAlCe-LDH on β-Ni(OH)2/Ni foam. Implementing a two-electrode configuration for the MgAlCe-LDH/β-Ni(OH)2/Ni foam, the total seawater splitting investigation exhibits 1.42 V cell voltage at a current density of 10 mA cm-2 and 25 h long-term stability.

Modulating the Electronic Structure of Cobalt-Vanadium Bimetal Catalysts for High-Stable Anion Exchange Membrane Water Electrolyzer

Modulating the electronic structure of catalysts to effectively couple the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential for developing high-efficiency anion exchange membrane water electrolyzer (AEMWE). Herein, a coral-like nanoarray composed of nanosheets through the synergistic layering effect of cobalt and the 1D guiding of vanadium is synthesized, which promotes extensive contact between the active sites and electrolyte. The HER and OER activities can be enhanced by modulating the electronic structure through nitridation and phosphorization, respectively, enhancing the strength of metal-H bond to optimize hydrogen adsorption and facilitating the proton transfer to improve the transformation of oxygen-containing intermediates. Resultantly, the AEMWE achieves a current density of 500 mA cm-2 at 1.76 V for 1000 h in 1.0 M KOH at 70 °C. The energy consumption is 4.21 kWh Nm-3 with the producing hydrogen cost of $0.93 per kg H2. Operando synchrotron radiation and Bode phase angle analyses reveal that during the high-energy consumed OER, the dissolution of vanadium species transforms distorted Co-O octahedral into regular octahedral structures, accompanied by a shortening of the Co-Co bond length. This structural evolution facilitates the formation of oxygen intermediates, thus accelerating the reaction kinetics.

Bifunctional Electrocatalysts for Overall and Hybrid Water Splitting

Electrocatalytic water splitting driven by renewable electricity has been recognized as a promising approach for green hydrogen production. Different from conventional strategies in developing electrocatalysts for the two half-reactions of water splitting (e.g., the hydrogen and oxygen evolution reactions, HER and OER) separately, there has been a growing interest in designing and developing bifunctional electrocatalysts, which are able to catalyze both the HER and OER. In addition, considering the high overpotentials required for OER while limited value of the produced oxygen, there is another rapidly growing interest in exploring alternative oxidation reactions to replace OER for hybrid water splitting toward energy-efficient hydrogen generation. This Review begins with an introduction on the fundamental aspects of water splitting, followed by a thorough discussion on various physicochemical characterization techniques that are frequently employed in probing the active sites, with an emphasis on the reconstruction of bifunctional electrocatalysts during redox electrolysis. The design, synthesis, and performance of diverse bifunctional electrocatalysts based on noble metals, nonprecious metals, and metal-free nanocarbons, for overall water splitting in acidic and alkaline electrolytes, are thoroughly summarized and compared. Next, their application toward hybrid water splitting is also presented, wherein the alternative anodic reactions include sacrificing agents oxidation, pollutants oxidative degradation, and organics oxidative upgrading. Finally, a concise statement on the current challenges and future opportunities of bifunctional electrocatalysts for both overall and hybrid water splitting is presented in the hope of guiding future endeavors in the quest for energy-efficient and sustainable green hydrogen production.

One-Dimensional La0.2Sr0.8Cu0.4Co0.6O3-δ Nanostructures for Efficient Oxygen Evolution Reaction

Producing oxygen and hydrogen via the electrolysis of water has the advantages of a simple operation, high efficiency, and environmental friendliness, making it the most promising hydrogen production method. In this study, La0.2Sr0.8Cu0.4Co0.6O3-δ (LSCC) nanofibers were prepared by electrospinning to utilize non-noble perovskite oxides instead of noble metal catalysts for the oxygen evolution reaction, and the performance and electrochemical properties of LSCC nanofibers synthesized at different firing temperatures were evaluated. In an alkaline environment (pH = 14, 6 M KOH), the nanofibers calcined at 650 °C showed an overpotential of 209 mV at a current density of 10 mA cm-2 as well as good long-term stability. Therefore, the prepared LSCC-650 NF catalyst shows excellent potential for electrocatalytic oxygen evolution.

Facile Synthesis of Co Nanoparticles Embedded in N-Doped Carbon Nanotubes/Graphitic Nanosheets as Bifunctional Electrocatalysts for Electrocatalytic Water Splitting

Developing robust and cost-effective electrocatalysts to boost hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs) is crucially important to electrocatalytic water splitting. Herein, bifunctional electrocatalysts, by coupling Co nanoparticles and N-doped carbon nanotubes/graphitic nanosheets (Co@NCNTs/NG), were successfully synthesized via facile high-temperature pyrolysis and evaluated for water splitting. The morphology and particle size of products were influenced by the precursor type of the cobalt source (cobalt oxide or cobalt nitrate). The pyrolysis product prepared using cobalt oxide as a cobalt source (Co@NCNTs/NG-1) exhibited the smaller particle size and higher specific surface area than that of the pyrolysis products prepared using cobalt nitrate as a cobalt source (Co@NCNTs/NG-2). Notably, Co@NCNTs/NG-1 displayed much lower potential -0.222 V vs. RHE for HER and 1.547 V vs. RHE for OER at the benchmark current density of 10 mA cm-2 than that of Co@NCNTs/NG-2, which indicates the higher bifunctional catalytic activities of Co@NCNTs/NG-1. The water-splitting device using Co@NCNTs/NG-1 as both an anode and cathode demonstrated a potential of 1.92 V to attain 10 mA cm-2 with outstanding stability for 100 h. This work provides a facile pyrolysis strategy to explore highly efficient and stable bifunctional electrocatalysts for water splitting.