Energy-efficient hydrogen production over a high-performance bifunctional NiMo-based nanorods electrode

Boosting urea-assisted water splitting over P-MoO2@CoNiP through Mo leaching/reabsorption coupling CoNiP reconstruction

Combining the urea oxidation reaction (UOR) with the hydrogen evolution reaction (HER) is an effective technology for energy-saving hydrogen production. Herein, a bifunctional electrocatalyst with CoNiP nanosheet coating on P-doped MoO2 nanorods (P-MoO2@CoNiP) is obtained via a two-step hydrothermal followed a phosphorization process. The catalyst demonstrates exceptional alkaline HER performance due to the formation of MoO2 and the dissolution/absorption of Mo. Meanwhile, the inclusion of Co and P in the P-MoO2@CoNiP catalyst facilitated the formation of NiOOH, enhancing UOR performance. Density functional theory calculations reveal that the hydrogen adsorption Gibbs free energy (ΔGH*) of P-MoO2@CoNiP is closer to 0 eV than CoNiP, favoring the HER. The catalyst only needs -0.08 and 1.38 V to reach 100 mA cm-2 for catalyzing the HER and UOR, respectively. The full urea electrolysis system driven by P-MoO2@CoNiP requires 1.51 V to achieve 100 mA cm-2, 120 mV lower than the traditional water electrolysis.

Highly Stable Mo-NiO@NiFe-Layered Double Hydroxide Heterojunction Anode Catalyst for Alkaline Electrolyzers with Porous Membrane

Heterostructure catalysts are considered as promising candidates for promoting the oxygen evolution reaction (OER) process due to their strong electron coupling. However, the inevitable dissolution and detachment of the heterostructure catalysts are caused by the severe reconstruction, dramatically limiting their industrial application. Herein, the NiFe-layered double hydroxide (LDH) nanosheets attached on Mo-NiO microrods (Mo-NiO@NiFe LDH) by the preoxidation strategy of the core NiMoN layer are synthesized for ensuring the high catalytic performance and stability. Owing to the enhanced electron coupling and preoxidation process, the obtained Mo-NiO@NiFe LDH exhibits a superlow overpotential of 253 mV to achieve a practically relevant current density of 1000 mA cm-2 for OER with exceptional stability over 1200 h. Notably, the overall water splitting system based on Mo-NiO@NiFe LDH reveals remarkable stability, maintaining the catalytic activity at a current density of 1000 mA cm-2 for 140 h under industrial harsh conditions. Furthermore, the Mo-NiO@NiFe LDH demonstrates outstanding activity and long-term durability in a practical alkaline electrolyzer assembly with a porous membrane, even surpassing the performance of IrO2. This work provides a new sight for designing and synthesizing highly stable heterojunction electrocatalysts, further promoting and realizing the industrial electrocatalytic OER.

A universal approach to dual-metal-atom catalytic sites confined in carbon dots for various target reactions

Here, a molecular-design and carbon dot-confinement coupling strategy through the pyrolysis of bimetallic complex of diethylenetriamine pentaacetic acid under low-temperature is proposed as a universal approach to dual-metal-atom sites in carbon dots (DMASs-CDs). CDs as the "carbon islands" could block the migration of DMASs across "islands" to achieve dynamic stability. More than twenty DMASs-CDs with specific compositions of DMASs (pairwise combinations among Fe, Co, Ni, Mn, Zn, Cu, and Mo) have been synthesized successfully. Thereafter, high intrinsic activity is observed for the probe reaction of urea oxidation on NiMn-CDs. In situ and ex situ spectroscopic characterization and first-principle calculations unveil that the synergistic effect in NiMn-DMASs could stretch the urea molecule and weaken the N-H bond, endowing NiMn-CDs with a low energy barrier for urea dehydrogenation. Moreover, DMASs-CDs for various target electrochemical reactions, including but not limited to urea oxidation, are realized by optimizing the specific DMAS combination in CDs.

Constructing interface engineering and tailoring a nanoflower-like FeP/CoP heterostructure for enhanced oxygen evolution reaction

The inexpensive and highly efficient electrocatalysts toward oxygen evolution reaction (OER) in water splitting electrolysis have displayed promising practical applications to relieve energy crisis. Herein, we prepared a high-yield and structurally regulated bimetallic cobalt-iron phosphide electrocatalyst by a facile one-pot hydrothermal reaction and subsequent low-temperature phosphating treatment. The tailoring of nanoscale morphology was achieved by varying the input ratio and phosphating temperature. Thus, an optimized FeP/CoP-1-350 sample with the ultra-thin nanosheets assembled into a nanoflower-like structure was obtained. FeP/CoP-1-350 heterostructure displayed remarkable activity toward the OER with a low overpotential of 276 mV at a current density of 10 mA cm^-2, and a low Tafel slope of only 37.71 mV dec^-1. Long-lasting durability and stability were maintained with the current with almost no obvious fluctuation. The enhanced OER activity was attributed to the presence of copious active sites from the ultra-thin nanosheets, the interface between CoP and FeP components, and the synergistic effect of Fe-Co elements in the FeP/CoP heterostructure. This study provides a feasible strategy to fabricate highly efficient and cost-effective bimetallic phosphide electrocatalysts.

Mott Schottky CoSx-MoOx@NF heterojunctions electrode for H2 production and urea-rich wastewater purification

The sluggish kinetics of oxygen evolution reaction (OER) is the bottleneck of alkaline water electrolysis. The urea oxidation reaction (UOR) with much faster kinetics was to replace OER. To further promote UOR, a heterojunction structure assembled of CoS_x and MoO_x was established, and then its superior catalytic activity was predicted by DFT calculation. After that, an ultra-thin CoS_x-MoO_x@nickel foam (CoS_x-MoO_x@NF) electrode with a Mott-Schottky structure was prepared via a facile hydrothermal method, followed by a low-temperature vulcanization. Results highlighted CoS_x-MoO_x@NF electrode presented a superior performance toward UOR, OER, and H₂ evolution reaction (HER). Notably, it exhibited excellent electrocatalytic performance for OER (1.32 V vs. RHE, 10 mA cm^-2), UOR (1.305 V vs. RHE, 10 mA cm^-2), and urea-assisted overall water splitting with a low voltage (1.38 V, 10 mA cm^-2) when CoS_x-MoO_x@NF electrode served as both anode and cathode. It is promising to use CoS_x-MoO_x@NF in an electrochemical system integrated with H₂ generation and urea-rich wastewater purification.

Interface engineering of core-shell Ni0.85Se/NiTe electrocatalyst for enhanced oxygen evolution and urea oxidation reactions

The development of highly efficient oxygen evolution reaction (OER) and urea oxidation reaction (UOR) electrocatalysts with abundant resources is necessary for green hydrogen production. Ni-based compounds have received attention as the most promising earth-abundant electrocatalysts for OER and UOR, whereas some compounds in this main group, e.g., nickel selenides and tellurides, have received little attention. Herein, we demonstrate the interfacial engineered Ni_0.85Se/NiTe array on Ni foam as a highly efficient catalyst for the OER, which exhibits an overpotential of 200 mV to obtain a current density of 10 mA cm^-2 in alkaline solutions. Meanwhile, it exhibits a low potential of 1.301 V for the UOR at a current density of 100 mA cm^-2. In particular, it even has the potential to be used in methanol oxidation reaction and ethanol oxidation reaction. The vertical NiTe array not only serves as the conductive substrate for highly improving the mass loading of Ni_0.85Se, but also triggers the strong electron interaction between two components, leading to increased adsorption sites available for the intermediates formed in the OER and UOR on the Ni_0.85Se surface. This study provides a broad avenue to construct hierarchical nanostructures as outstanding electrocatalysts for efficient OER and UOR.

Boosting Hydrazine Oxidation Reaction on CoP/Co Mott-Schottky Electrocatalyst through Engineering Active Sites

The hydrazine oxidation reaction (HzOR), as a substitute for the sluggish oxygen evolution reaction (OER), is identified as a promising powerfrugal strategy for hydrogen production through water splitting. However, the HzOR activity of the present electrocatalysts is unsatisfying because the work potential is much higher than the theoretical value. Herein, we design a typical Mott-Schottky electrocatalyst consisting of CoP/Co nanoparticles for the HzOR, which exhibits remarkable HzOR activity with ultralow potentials of -69 and 177 mV at 10 and 100 mA cm^-2, respectively. It stands out in a range of cobalt-based materials and is even comparable to some precious-metal-based materials composed of Pt or Ru. A shown by with structural characterization and density functional theory (DFT) calculations, the interfaces between CoP/Co nanoparticles not only provide the active sites of HzOR but also promote the multistep dehydrogenation reaction of N₂H₄, thus enhancing the HzOR activity.

Coaxial Ni-S@N-Doped Carbon Nanofibers Derived Hierarchical Electrodes for Efficient H2 Production via Urea Electrolysis

Electrochemical water splitting into hydrogen is a promising strategy for hydrogen production powered by solar energy. However, the cell voltage of an electrolyzer is still too high for practical application, which is mainly limited by the sluggish oxygen evolution reaction process. To this end, hybrid water electrolyzers have drawn tremendous attention. Herein, coaxial Ni/Ni₃S₂@N-doped nanofibers are directly grown on nickel foam (NF), which is highly active for hydrogen evolution reaction. Meanwhile, the Ni₃S₂@N-doped nanofibers on NF prepared in an Ar atmosphere display superior urea oxidation reaction performance to previously reported catalysts. The cell voltage is about 1.50 V in urea electrolysis to deliver a current density of 20 mA cm^-2, lower than that of a traditional water electrolyzer (1.82 V). The current density is around 77% relative to its initial value of 20 mA cm^-2 after 20 h, superior to Pt/C|Ir/C-based urea electrolysis (14%). It is found that the synergistic effect between metallic Ni and Ni₃S₂, as well as the interfacial effect between metal centers and N-doped carbon, favors the initial dissociation of H₂O and the adsorption/desorption of H* with thermal neutral Gibbs free energy. Meanwhile, the in-situ generated NiOOH on the outer surface of Ni₃S₂ possessed lower electrochemical activation energy for urea decomposition. Meanwhile, the abundant oxygen vacancies in electrodes could expose more active sites for the adsorption of intermediates, including H* and OOH*. It is also found that the hierarchical nanostructure of densely packed nanowires provides ideal electronic and ionic transport paths for fast electrocatalytic kinetics. The present work indicated that the modulation of compositions and hierarchical nanostructure is effective to prepare efficient catalysts for H₂ production via urea electrolysis.

Pt modified Ni–Mo-based hydrates as bifunctional electrocatalysts for overall water splitting

Pt-Modified Ni–Mo-based nanomaterials were prepared by a simple and effective method.

Interface engineering of NiV-LDH@FeOOH heterostructures as high-performance electrocatalysts for oxygen evolution reaction in alkaline conditions

A hybrid heterostructure eletrocatalyst supported on Ni foam is facilely synthesized as a high-performance OER electrocatalyst for alkaline water electrolysis. Compared to their pristine NiV-LDH counterpart, the self-made NiV-LDH@FeOOH heterostructures exhibit an extremely low overpotential of ∼297 mV at 100 mA cm^-2 current output, and excellent long-term durability.