Enhancing hydrogen evolution through urea electrolysis over Co-doped Ni-P-O film on nickel foam

Recent advances in amorphous metal phosphide electrocatalysts for hydrogen evolution reaction

Recent advances in transition-metal phosphide electrocatalysts: Synthetic approach, improvement strategies and environmental applications

The requirements for beneficial materials restructuring into
a higher performance OER electrocatalyst are still a largely open question.
Here we use Erythrite (Co3(AsO4)2 8H2O)
as a Co-based OER electrocatalyst to evaluate its catalytic properties during in-situ
restructuring into an amorphous Co-based catalyst in four different
electrolytes at pH 7. Using diffraction, microscopy and spectroscopy, we
observed a strong effect in the restructuring kinetics depending of the anions
in the electrolyte. Only carbonate electrolyte could activate the catalyst electrode,
which we relate to its slow restructuring kinetics. While its turnover
frequency (TOF) reduced from 2.84 O2 Co-1 s-1
to a constant value of 0.10 O2 Co-1 s-1 after
~ 300 cycles, the number of redox active sites continuously increased, which
explained the current increase of around 100%. The final activated material
owns an adequate local order, a high Co oxidation state and a high number of
redox-active Co ions, which we identify as the trinity for enhancing the OER
activity. Thus, this work provides new insights into for the rational design of
high-performance OER catalysts by electrochemical restructuring.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/aenm.202101737

Requirements for Beneficial Electrochemical Restructuring: A Model Study on a Cobalt Oxide in Selected Electrolytes

Catalytic electrode assisted water electrolysis is a potential method of clean hydrogen production. The present work deals with the surface modification of Ni-P electrode (NPE) by electroless co-deposition of cubic phased cobalt oxide, for enhanced hydrogen evolution from 1 M NaOH solution. The excellent coating thickness (9–10 µm), hardness (547 HVN) and wear resistant properties of 5 g/L Co3O4 deposited Ni-P divulge its appropriateness for industrial use. The co-operative interaction of cubic phased Co3O4 with Ni and P improves the interfacial charge transfer reaction (lower Rct of 66 Ω) and cause HER at a reduced overpotential (71 mV at 10 mA/cm2). The mild steel supported NPE/Co3O4 coating is highly porous and conductive. And the evolution of hydrogen from 1 M NaOH solution is kinetically controlled by Volmer process. The mechanism of entire catalyst assisted water splitting follows Volmer-Tafel route. The activity of the electrode was thoroughly evaluated. Furthermore the continuous evolution of hydrogen for a period of 50 h by the metal oxide modified NPE, reiterate the sustainability of electro activity. The implemented surface engineering strategy for Ni-P electrode by the spinel structured cubic phased Co3O4 co-deposition to get a rough and porous surface morphology is by a relatively less expensive electroless deposition method. The excellent value for electro catalytically active surface area (ECSA = 93.14 cm2) and long term activity in alkaline solution made NPE/5 g/L Co3O4, a competent catalytic electrode for HER.

Surface engineering of Ni-P electrode by cobalt oxide co-deposition for electrochemical hydrogen evolution reaction

As a kind of catalyst with great development potential, the nickel–phosphorus (Ni–P) catalyst is widely studied. However, the difference in catalytic performance between the amorphous and crystalline Ni–P electrodes in hydrogen evolution still lacks the necessary research. Herein, an amorphous Ni–P electrode was prepared by a method of cathodic electrodeposition, and showed excellent catalytic performance, achieving a HER current density of 10 mA cm−2 in 1.0 M KOH solution at an overpotential of 50 mV. Meanwhile, it was converted to a crystalline Ni–P electrode by annealing under vacuum. On this basis, we have compared the differences in the catalytic performance of the crystalline and amorphous Ni–P electrodes in alkaline and acidic environments. It was found that amorphous Ni–P showed excellent hydrogen evolution catalytic performance in alkaline electrolytes, which was mainly due to the better hydrophilicity and higher inherent catalytic activity of the amorphous state. But it was not stable, so the performance was not satisfactory in acidic solution. On the other hand, the inherent catalytic activity and hydrophilicity of crystalline Ni–P are somewhat worse than those of amorphous Ni–P, and the catalytic performance was not as good as that of the latter, but due to the stable chemical state, crystalline Ni–P had better stability in acidic solutions.

High-efficiency Ni–P catalysts in amorphous and crystalline states for the hydrogen evolution reaction

As nonprecious metal catalysts, transition metal phosphides (TMPs) are well known for their hydrogen evolution performance, but their low oxygen evolution reaction activity inhibits their ability to serve as excellent dual-functional catalysts. In this study, a bimetallic phosphide electrocatalyst with nanowire morphology was prepared using a simple and controllable etch-doping strategy with nickel foam (NF) as the carrier of the integrated electrode. The morphology of the catalyst nanowires offers a relatively high specific surface area, thereby providing more active sites and promoting the contact between the electrolyte and the catalyst. Electrochemical tests show that Co1Fe0.1P/NF exhibits excellent performance and stability for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). For the HER, the catalyst needs an overpotential of only 73 mV in 1 M KOH to reach a current density of 10 mA cm-2 and an overpotential of only 257 mV for the OER. It is worth noting that when using Co1Fe0.1P/NF as the cathode and anode for electrolyzing water in the electrolyzer system, a current density of 10 mA cm−2 can be reached with only 1.60 V. This research provides an effective synthesis route for transition metal phosphides as bifunctional catalysts for water electrolysis.

An etch-doping strategy: cobalt–iron bimetallic phosphide as a bifunctional electrocatalyst for highly efficient water splitting

In recent years, the catalyst efficiency of hydrogen evolution reaction (HER) has been extensively studied. However, the stability of catalysts at high current densities is still a challenge. Herein, layered Ni−Co−P was electrodeposited on carbon fiber paper (CFP) via cyclic voltammetry (CV). This low‐cost electrode exhibits high efficiency and excellent durability for HER in 1 M KOH. To achieve current densities of 10, 100, 500, and 1000 mA cm−2, Ni−Co−P/CFP required overpotentials of 49, 95, 170, and 295 mV, respectively. The layered structure allows the catalyst to fall off layer by layer. After the outer layer of catalyst falls off, the inner layer of catalyst will be exposed to continue working. After 300 h of HER at 1000 mA cm−2, Ni−Co−P/CFP still has a regular morphology and high efficiency. Our work shows that layered Ni−Co−P/CFP has excellent prospects for practical applications.

Xuan Zhao

Papers

High-efficiency Ni–P catalysts in amorphous and crystalline states for the hydrogen evolution reaction

An etch-doping strategy: cobalt–iron bimetallic phosphide as a bifunctional electrocatalyst for highly efficient water splitting

Layered Ni−Co−P Electrode Synthesized by CV Electrodeposition for Hydrogen Evolution at Large Currents