Optimization of Ni−Co−Fe‐Based Catalysts for Oxygen Evolution Reaction by Surface and Relaxation Phenomena Analysis

Abstract

Trimetallic double hydroxide NiFeCo−OH is prepared by coprecipitation, from which three different catalysts are fabricated by different heat treatments, all at 350 °C maximum temperature. Among the prepared catalysts, the one prepared at a heating and cooling rate of 2 °C min−1 in N2 atmosphere (designated NiFeCo−N2‐2 °C) displays the best catalytic properties after stability testing, exhibiting a high current density (9.06 mA cm−2 at 320 mV), low Tafel slope (72.9 mV dec−1), good stability (over 20 h), high turnover frequency (0.304 s−1), and high mass activity (46.52 A g−1 at 320 mV). Stability tests reveal that the hydroxide phase is less suitable for long‐term use than catalysts with an oxide phase. Two causes are identified for the loss of stability in the hydroxide phase: a) Modeling of the distribution function of relaxation times (DFRT) reveals the increase in resistance contributed by various relaxation processes; b) density functional theory (DFT) surface energy calculations reveal that the higher surface energy of the hydroxide‐phase catalyst impairs the stability. These findings represent a new strategy to optimize catalysts for water splitting.

NiMoO4@Co3O4 Core–Shell Nanorods: In Situ Catalyst Reconstruction toward High Efficiency Oxygen Evolution Reaction

“…[28][29][30][31] For the case of Co 3 O 4, we could not see any redox reaction peak related to any Co 2+ / Co 3+ and Co 3+ /Co 4 redox couple (Figure S9a, Supporting Information), consistent with related works. [32][33][34] Hydrous NiMoO 4 contains two types of water molecules: surface water and coordinated water. [9] The surface water, including some portion of lattice water, should be removed when the annealing temperature is above 100 °C.…”

What is Next in Anion‐Exchange Membrane Water Electrolyzers? Bottlenecks, Benefits, and Future

“…[111] Therefore, carbides (e. g., Mo 2 C), spinels, oxides, perovskites, and ceramic materials are the most promising PGM-free electro- catalysts considering the tradeoff between performance and durability. [111][112][113][114][115][116][117][118] Sub-stoichiometric metal oxides, carbides, and nitrides seems to be excellent electrocatalysts as they are expected to keep their structure even under high oxidative potentials. In addition, core-shell structures with conductive cores are suitable, allowing good electronic conductivity while protecting the core from oxidation.…”

“…Therefore, carbides (e. g., Mo 2 C), spinels, oxides, perovskites, and ceramic materials are the most promising PGM‐free electrocatalysts considering the tradeoff between performance and durability [111–118] . Sub‐stoichiometric metal oxides, carbides, and nitrides seems to be excellent electrocatalysts as they are expected to keep their structure even under high oxidative potentials.…”

Exploring the mechanism of the excellent catalytic activity of NiFe-layered double hydroxides in oxygen evolution reactions by modifying the iron content

“…This structure is conducive to the activity and stability of the sample. 21,22 We also used electrochemical impedance spectroscopy (EIS) to evaluate the charge transferability in different samples. As shown in Figure S5(a) in the Supporting Information, R s is the electrolyte resistance, R p is the charge-transfer resistance, and CPE is a constant-phase element.…”