Recent advances in methods and technologies for enhancing bubble detachment during electrochemical water splitting

Development of new electrocatalysts with high electrocatalytic activity and stability is of great importance in the production of hydrogen fuel. Numerous methods have been established to increase the activity of electrocatalysts, including increasing active surface area and improving intrinsic catalytic activity. However, the electrochemical water splitting is a gas-involving reaction in which hydrogen and oxygen bubbles are formed on cathode and anode surfaces, respectively, which lead to an increase in overpotential of electrochemical reactions. In this review, recent advances have been complied to understand the behavior of hydrogen and oxygen bubbles separation from the surface of electrodes during water splitting. Initially, various types of resistance in water splitting have been discussed, and further progress has been discussed to improve the separation of bubbles and thus improve electrocatalytic activity. These improvements include surface nanostructuring and making superaerophobic surfaces where bubbles can easily be removed from the surface, resulting in lower bubble resistance. Furthermore, the use of magnetic, supergravity and ultrasonic fields are among additional methods for fast separation of bubbles from the surface and improving catalytic activity This paper presents a review of a research pathway for creating 3D nanoarrays to improve the bubble separation behavior on the surface and improve electrocatalytic properties. © 2019 Elsevier Ltd1

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. © 2020 American Chemical Society.FALS

Electrodeposition of self-supported transition metal phosphides nanosheets as efficient hydrazine-assisted electrolytic hydrogen production catalyst

The synthesis of electrocatalysts which used simultaneously as electrodes for the hydrazine oxidation reaction (HzOR), and hydrogen evolution reaction (HER) can significantly improve the efficiency of hydrogen production in the water splitting process. Here, Ni–Co–Fe–P binder-free nanosheets were fabricated using the electrochemical deposition method and used as an effective, stable, and cost-effective electrode for hydrazine-assisted electrochemical hydrogen production. Taking advantage of high surface area, being binder-free, and synergistic effect between the elements in the electrode composition, this electrode showed unique electrocatalytic activity and stability. When this electrode was used as a bifunctional electrode for HzOR-HER, a cell voltage of 94 mV was required to reach a current density of 10 mA cm−2. The results of this study indicated that the Ni–Co–Fe–P electrode is an excellent candidate for the hydrogen production industry. © 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.FALS

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. © 2019 The Royal Society of Chemistry.1

Highly Active and Durable NiCoSeP Nanostructured Electrocatalyst for Large-Current-Density Hydrogen Production

Large-scale hydrogen production via electrochemical water splitting requires low-cost and efficient electrocatalysts that work well at high current densities with a low overpotential for the hydrogen evolution reaction (HER). Herein, we report the production of a NiCoSeP nanostructured electrocatalyst by a low-cost, one-step electrodeposition technique. The catalyst exhibits very high current densities at small overpotentials (100 mA cm-2 at 151 mV, 500 mA cm-2 at 286 mV, and 1000 mA cm-2 at 381 mV) in 1.0 M KOH electrolyte. Moreover, NiCoSeP shows excellent HER performance in an acidic medium with small overpotentials of 93 and 131 mV to deliver large current densities of 100 and 500 mA cm-2, respectively. The unique morphology of NiCoSeP, superhydrophilic, and superaerophobic properties could facilitate electrolyte diffusion and rapid delivery of the generated bubble, respectively. Our experimental data confirm that the advantages of the excellent HER activity and stability of NiCoSeP nanostructure originate from the high active surface area, bimetal double-anion effect, and enhanced mass transfer of reactants and hydrogen bubbles. This work may provide a promising way for rational design and simplify the synthesis process of practical electrocatalysts. © 2021 American Chemical Society. All rights reserved.1

Electrodeposited Ni-Co-P hierarchical nanostructure as a cost-effective and durable electrocatalyst with superior activity for bifunctional water splitting

Designing earth-abundant, cost-effective catalysts with superior performance for electrochemical water splitting is among the essential global challenges. In this study, amorphous Ni[sbnd]Co[sbnd]P coatings are applied on nickel nanocones array using the cyclic voltammetry electrodeposition method in different cycles and nickel-to-cobalt ratios. The electrocatalytic activities of the as-fabricated electrodes are studied for hydrogen evolution reaction and oxygen evolution reaction in alkaline and neutral solution. The three-dimensional nickel nanocones expose more active surface area for hydrogen evolution reaction and oxygen evolution reaction. Binder-free Ni[sbnd]Co[sbnd]P@nickel nanocones electrode exhibits superior hydrogen evolution reaction catalytic activity in the alkaline solution, which requires only 51 and 110 mV for delivering 10 and 100 mAcm −2 , respectively. Also, this electrode exhibits low oxygen evolution reaction overpotential of 221 mV and 254 mV at 10 and 100 mAcm −2 , respectively. The fabricated electrode is able to sustain the current density of 100 mAcm -2 with negligible degradation in overpotential which shows remarkable electrochemical stability. Moreover, this active and stable bifunctional electrocatalyst is used for full water splitting, able to deliver the current density of 10 mAcm −2 in 1.53 V. Also, the fabricated electrode represented favorable behaviors as electrocatalyst for both HER and OER in neutral solution. © 2019 Elsevier B.V.1

Binder-free P-doped Ni-Se nanostructure electrode toward highly active and stable hydrogen production in wide pH range and seawater

Transition metal selenide materials are extensively investigated as electrocatalysts for the hydrogen evolution reaction (HER). Despite having good electrical transportability, they suffer from low abundance catalytic active sites and relatively poor long-term stability. Herein, we demonstrate phosphorous doping in NiSe as an effective strategy to simultaneously boost electrocatalytic activity and stability. The phosphorous doped NiSe catalyst needs the lowest overpotentials of 90,101, 212, and 296 mV at 10 mAcm(-2) in alkaline, acidic, neutral, and seawater electrolytes, respectively, as well as continuous stable operation over 100 h. The high exchange current density of 1.379 mAcm(-2), the excellent mass activity of 23.95 Ag-1, and a turnover frequency (TOF) value of 0.339 s(-1) at 150 mV indicate the promising electrocatalytic HER performance of the P-doped NiSe catalyst. Our experimental data and theoretical calculations confirm that the advantage of HER activity and stability of P-doped NiSe originates from enriched catalytic active sites with near-zero H adsorption free energy and tuned electronic structure. This work provides a blueprint for the design and synthesis of best-in-class selenide-based HER & nbsp;catalysts.FALS

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

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