In Situ Assembly of a Superaerophobic CoMn/CuNiP Heterostructure as a Trifunctional Electrocatalyst for Ampere-Level Current Density Urea-Assisted Hydrogen Production.

Urea electrolysis is a promising energy-efficient hydrogen production process with environmental benefits, but the lack of efficient and sustainable ampere-level current density electrocatalysts fabricated through simple methods is a major challenge for commercialization. Herein, we present an efficient and stable heterostructure electrocatalyst for full urea and water electrolysis in a convenient and time-efficient preparation manner. Overall, superhydrophilic/superaerophobic CoMn/CuNiP/NF exhibits exceptional performance for the hydrogen evolution reaction (HER) (-33.8, -184.4, and -234.8 mV at -10, -500, and -1000 mA cm-2, respectively), urea electro-oxidation reaction (UOR) [1.28, 1.43, and 1.51 V (vs RHE) at 10, 500, and 1000 mA cm-2, respectively], and oxygen evolution reaction (OER) [1.45, 1.67, and 1.74 V (vs RHE) at 10, 500, and 1000 mA cm-2, respectively]. Moreover, the superaerophobic CoMn/CuNiP/NF demonstrates promising potential in full urea (1.33, 1.57, and 1.60 V at 10, 500, and 1000 mA cm-2, respectively) and water (1.46 V, 1.78, and 1.86 at 10, 500, and 1000 mA cm-2, respectively) electrolysis. Based on X-ray photoelectron spectroscopy results, it was determined that the surface of the CoMn/CuNiP electrode was rich in redox pairs such as Ni2+/Ni3+, Cu+/Cu2+, Co2+/Co3+, and Mn2+/Mn3+, which are crucial for the formation of active sites for the OER and UOR, such as NiOOH, MnOOH, and CoOOH, thereby enhancing the catalytic activity. Besides, the in situ assembled CoMn/CuNiP/NF displayed highly stable performance for HER, OER, and UOR with high Faradaic efficiency for over 500 h. This research offers a simple and efficient method for manufacturing a high-efficiency and stable trifunctional electrocatalyst capable of delivering ampere-level current density in urea-assisted hydrogen production. Our density functional theory calculations reveal the potential of CoMn/CuNiP as an effective catalyst, enhancing the electronic properties and catalytic performance. The near-zero Gibbs free-energy change for HER underscores its promise, while reduced CO2 desorption energies and charge redistribution support efficient UOR. These findings signify CoMn/CuNiP's potential for electrochemical applications.

Electrosynthesis of Superhydrophilic Nickel Nanosheets on a Three-Dimensional Microporous Template: Applicability toward MOR.

In this report, a nickel nanoscaled morphology was synthesized by two-step cathodic electrodeposition on a microporous copper template. The resulting morphology, nanosheets formed on 3D micropores, offers incredible cyclic stability of almost 100% and facilitates transport mechanisms while significantly preserving the active surface area. The origin of the nanosheets is assumed to be the presence of a small amount of iron cations in the electrolyte bath during the final deposition step. By altering the deposition current density of this step, three samples were prepared and compared in terms of the resulting morphology, chemical composition, surface area, wettability, and activation toward the methanol oxidation Reaction. Results show that an increase in the deposition current density in the range of this study produces finer and denser nanosheets, a higher content of reduced iron, a larger surface area, and greater activity toward MOR. The current density for methanol oxidation was exceptional among all other studies on nickel-containing electrocatalysts, yielding a steady-state current density of 135 mA cm-2 at 600 mV versus SCE. All samples offered superhydrophilicity.

Mn-incorporated nickel selenide: an ultra-active bifunctional electrocatalyst for hydrogen evolution and urea oxidation reactions.

We report Ni-Mn-Se supported on Ni foam as a highly active and stable bifunctional electrocatalyst that exhibits overpotentials of 28 and 122 mV to reach a current density of 10 mA cm-2 for the hydrogen evolution reaction (HER) and urea oxidation reaction (UOR), respectively, and maintains its stability for over 50 h in both reactions. In addition, an overall urea splitting cell voltage of 1.352 V is needed at the current density of 10 mA cm-2 for the optimized electrode.

Pulse Electrodeposition of a Superhydrophilic and Binder-Free Ni-Fe-P Nanostructure as Highly Active and Durable Electrocatalyst for Both Hydrogen and Oxygen Evolution Reactions.

Development and fabrication of electrodes with favorable electrocatalytic activity, low-cost, and excellent electrocatalytic durability are one of the most important issues in the hydrogen production area using the electrochemical water splitting process. We use the pulse electrodeposition method as a versatile and cost-effective approach to synthesize three-dimensional Ni-Fe-P electrocatalysts on nickel nanostructures under various applied frequencies and duration times, in which nanostructures exhibit excellent intrinsic electrocatalytic activity. Benefiting from the three-dimensional structure, as well as the simultaneous presence of the three elements nickel, iron, and phosphorus, the electrode fabricated at the optimal conditions has indicated outstanding electrocatalytic activity with a η10 of 66 and 198 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, in a 1.0 M KOH solution. Also, the water electrolysis cell constructed with this electrode and tested as a bifunctional electrode exhibited 1.508 V for 10 mA cm-2 in overall water splitting. In addition, the lowest amount of potential change in 100 mA cm-2 was observed for HER and OER, indicating excellent electrocatalytic stability. This study proposes a binder-free and economical technique for the synthesis of three-dimensional electrocatalysts.

Electrodeposition of Ni-Co-Fe mixed sulfide ultrathin nanosheets on Ni nanocones: a low-cost, durable and high performance catalyst for electrochemical water splitting.

The development of a bi-functional active and stable catalyst for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is an important challenge in overall electrochemical water splitting. In this study, firstly, nickel nanocones (NNCs) were formed using electrochemical deposition, and then Ni-Co-Fe based mixed sulfide ultrathin nanosheets were obtained by directly depositing on the surface of the nanocones using the CV method. With a hierarchical structure of Ni-Fe-Co-S nanosheets, not only was a high active surface area created, but also the electron transfer and mass transfer were enhanced. This structure also led to the faster release of hydrogen bubbles from the surface. An overpotential value of 106 mV was required on the surface of this electrode to generate a current density of 10 mA cm-2 in the HER, whereas, for the OER, 207 mV overpotential was needed to generate a current density of 10 mA cm-2. Furthermore, this electrode required 1.54 V potential to generate a current density of 10 mA cm-2 in the total electrochemical water splitting. The resulting electrode also exhibited reasonable electrocatalytic stability, and after 10 hours of electrolysis in the overall water splitting reaction, the voltage change was negligible. This study introduces a simple, efficient, reasonable and cost-effective method of creating an effective catalyst for the overall water splitting process.