Phase Diversity of Nickel Phosphides in Oxygen Reduction Catalysis

Abstract

Motivated by the challenge to find a low-cost catalyst with high activity for the oxygen reduction reaction (ORR), transition metal phosphides (TMPs) appear to be one of the most burgeoning alternatives to noble metal based electrocatalysts. In addition to the low cost, TMPs have numerous interesting features such as high conductivity and chemical stability. Since, the catalytic activity of TMPs is highly dependent on the metal/phosphorous ratio, herein, we report the investigation of nickel-phosphide/ carbon composites of different stoichiometries (Ni x P y /C) with tractable nickel phosphide phases as promising electrocatalyst for ORR under alkaline and acidic conditions. The Ni x P y /C composites are obtained by carbonization of a Ni-struvite (NiNH 4 PO 4 · H 2 O) coated phenol-formaldehyde resin at different temperatures, resulting in variations of the formed Ni x P y phases. As expected, it is found that the electrocatalytic ORR performance of the Ni x P y /C composites highly depends on the predominant phase of nickel phosphide formed. The highest catalytic activity for ORR in alkaline as well as acidic media was found for the Ni x P y /C composite with the highest proportion of Ni 2 P as a predominant phase, obtained at 800 8C. For composites with NiP 2 and Ni 12 P 5 as the predominant phase, obtained at lower and higher temperatures, respectively, a lower catalytic activity was found.

Coordination Engineering of Single‐Atom Catalysts for the Oxygen Reduction Reaction: A Review

“…But, the scarcity and high cost of Pt greatly restrict the widespread of these energy conversion devices. [ 6 ] Noble‐metal‐free catalysts are promising alternatives, and huge efforts have been devoted to the development of catalysts comprising only earth‐abundant elements, including transition‐metal (TM) oxides, [ 7–11 ] nitrides, [ 12–16 ] carbides, [ 17–21 ] phosphides, [ 22–24 ] sulfides, [ 25–29 ] selenides, [ 30–34 ] borides, [ 35 ] and metal‐free carbon materials. [ 36–38 ] Since Qiao et al.…”

Elucidating the Performance Limitations of Alkaline Electrolyte Membrane Electrolysis: Dominance of Anion Concentration in Membrane Electrode Assembly

“…The increase of O content can be due to the OH À adsorption during the electrochemical testing and eventually formation of Ni(OH) 2 . [43][44][45] However, as can be seen from SEM images in Figure S2b, S2d of SI and 6b and 6d, the sponge-like porous morphology of NiAl-AT and NiAlMo-AT electrodes is well retained after the durability test, despite partial oxidation and formation of partially Ni oxide or hydroxide, indicating the dimensional robustness of these electrodes. Figure 7a, presents a comparison between the experimental and theoretical polarization data obtained for AEMWE cells with APS-based electrodes at different KOH concentrations.…”

“…However, the EDX analysis of NiAlMo‐AT shown in Figure d, exhibits the increase of light blue color in the EDX images in the oxygen mapping compare to that of NiAlMo before durability test (Figure S2d of SI), which is overlapping with the space covered with Ni (red). The increase of O content can be due to the OH − adsorption during the electrochemical testing and eventually formation of Ni(OH) 2 . However, as can be seen from SEM images in Figure S2b, S2d of SI and 6b and 6d, the sponge‐like porous morphology of NiAl‐AT and NiAlMo‐AT electrodes is well retained after the durability test, despite partial oxidation and formation of partially Ni oxide or hydroxide, indicating the dimensional robustness of these electrodes.…”

“…After KOH activation, O content increases from 3.48 for NiAl‐BA to 13.52 wt.% for NiAl‐AA and from 5.47 for NiAlMo‐BA to 13.42 wt.% for NiAlMo‐AA. The initial presence of O can be due to plasma spraying in the air and an increase of O content after activation can be due to the OH − adsorption during the KOH activation process and eventually the formation of Ni (OH) 2 and also catalyst surface passivation …”

Synthesis of Flower‐Like Carbon‐Doped Nickel Phosphides Electrocatalysts for Oxygen Evolution Reaction

“…It can be seen that the intensity of D band is lower than G band. Since a smaller value of I D / I G means a higher degree of order in carbon and corresponds to a higher electrical conductivity, the NiP/C‐850 catalyst is expected to has an enhanced electrical conductivity.…”