Oxygen Evolution Catalyzed by Nickel–Iron Oxide Nanocrystals with a Nonequilibrium Phase

Abstract

Mixed nickel-iron oxides are of great interest as electrocatalysts for the oxygen evolution reaction (OER), the kinetically challenging half-reaction required for the generation of hydrogen gas from water via electrolysis. Previously, we had reported the synthesis of single crystal, soluble nickel-iron oxide nanoparticles over a wide range of nickel:iron compositions, with a metastable cubic rock salt phase ([Ni,Fe]O) that can be isolated despite the low solubility of iron in cubic nickel oxide at ambient temperatures. Here, activity for OER was examined, catalyzed by these [Ni,Fe]O nanoparticles integrated with indium tin oxide (ITO) electrodes. Because the as-prepared [Ni,Fe]O nanoparticles are oleate-capped, the surface ligands needed to be removed to induce adherence to the ITO substrate, and to enable charge transfer and contact with water to enable OER catalysis. Two different approaches were taken to reduce or eliminate the coverage of oleate ligands in these films: UV irradiation (254 nm) and air plasma. UV irradiation proved to lead to better results in terms of stable and OER-active films at pH 13. Kinetic analysis revealed that the Tafel slopes of these nanoparticle [Ni,Fe]O OER electrodes were limited by the electrochemical surface area and were found to be within the range of 30 to 50 mV/decade. Across the four compositions of Ni:Fe studied, from 24:76 to 88:12, the observed overpotential at 10 mA/cm2 for the OER in basic conditions decreased from 0.47 to 0.30 V as the proportion of nickel increased from 24% to 88%.

Template-free synthesis of mesoporous manganese oxides with catalytic activity in the oxygen evolution reaction

“…This is not observed in the case of the least active materials, thus indicating that high OER activity is associated to a defect-rich metastable oxide phase in agreement with other oxides with reported high activity in the OER. 68 Finally, the Mn-380 also exhibits the largest surface area which is also consistent with this being the most active of the oxides examined. The Mn-450 shows a very slight increase in the amount of Mn 2 O 3 , based on its XRD pattern, when compared to the Mn-380 and a slight decrease in the BET surface area.…”

Synthesis of a Highly Efficient Oxygen‐Evolution Electrocatalyst by Incorporation of Iron into Nanoscale Cobalt Borides

“…The benchmark catalysts for the OER are still noble metal catalysts, namely IrO 2 in acidic and RuO 2 in alkaline media. [18,19,24,27,[31][32][33][34][35][36][37][38] While the mechanisms of single metal catalysts are understood quiet well, the mechanism and the synergyo fb imetallic systems are less explored. Mn, [20][21][22][23][24] Fe, [24][25][26][27] Co, [6,24,[26][27][28] Ni, [24,26,27,29] and Cu [30] )a nd mixtures of such compounds.…”

“…[18,19,24,27,[31][32][33][34][35][36][37][38] While the mechanisms of single metal catalysts are understood quiet well, the mechanism and the synergyo fb imetallic systems are less explored. [24,[33][34][35][36]42] Smalla mounts of Fe incorporationi mprovedt he OER performance of the Ni-based compound dramatically.S imilar studies showed that the incorporation of Fe into Co 3 O 4 led to an improvement of the catalytic performance. [39][40][41] The energy required for each of these steps is different, and it furtherv aries depending on the catalystc hosen.…”

“…Mn, [20][21][22][23][24] Fe, [24][25][26][27] Co, [6,24,[26][27][28] Ni, [24,26,27,29] and Cu [30] )a nd mixtures of such compounds. [18,19,24,27,[31][32][33][34][35][36][37][38] While the mechanisms of single metal catalysts are understood quiet well, the mechanism and the synergyo fb imetallic systems are less explored. Rossmeisl et al showed that four consecutive energy steps are needed to create oxygen out of water.…”

“…Recent studies showedt hat one of these beneficial mixedmetal oxide systemsi saN i-based catalyst mixed with Fe. [24,[33][34][35][36]42] Smalla mounts of Fe incorporationi mprovedt he OER performance of the Ni-based compound dramatically.S imilar studies showed that the incorporation of Fe into Co 3 O 4 led to an improvement of the catalytic performance. [43,44] More recently Burke et al stated that the incorporation of Fe into CoOOH enhances the intrinsic activity by af actor of 100.…”