The two reactions at the heart of the work, the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), are notoriously sluggish. They involve four-electron transfers and multiple bond-breaking and bond-forming steps, which makes them the kinetic bottlenecks of water electrolyzers, fuel cells and rechargeable metal-air batteries. The benchmark catalysts, iridium dioxide and ruthenium dioxide, perform superbly but are scarce, expensive and prone to degradation over long operating lifetimes. That combination has pushed researchers toward earth-abundant transition-metal oxides, and perovskite oxides of the general formula ABO3 have emerged as one of the most tunable platforms, since nearly every element in the structure can be swapped to adjust electronic and catalytic properties.

The team chose a cobalt-free composition deliberately. Cobalt-containing perovskites such as BSCF and LSCF have long been favorites in the field, but cobalt raises cost and toxicity concerns. Their parent material, LSFC, combines lanthanum and strontium on the A-site with iron and copper on the B-site. Nickel was introduced at the B-site because it can access both Ni2+ and Ni3+ oxidation states, a redox flexibility that can reshape the local electronic environment around metal-oxygen bonds and influence how easily electrons move during oxygen chemistry. Using a glycine-assisted sol-gel route, the researchers prepared a full series of compositions, La0.5Sr0.5Fe1-xNixCu0.2O3 with x ranging from 0 to 0.8, by dissolving stoichiometric metal salts, gelling the solution with glycine, combusting the gel at 200 degrees Celsius and calcining the resulting ash at 900 degrees Celsius for four hours.

Structural analysis by powder X-ray diffraction with Le Bail full-profile fitting revealed a more complex picture than an ideal single-phase perovskite. Every sample contained a dominant tetragonal LSFC phase alongside an orthorhombic perovskite phase and a substantial fraction of an oxygen-vacancy-ordered strontium iron oxide, Sr8Fe8O23, whose proportion varied non-monotonically between roughly 31 and 53 percent as nickel content increased. The authors are careful to note that this multiphase character means the catalytic response reflects the combined contributions of all coexisting phases and their interfaces, not nickel substitution alone. Nevertheless, the diffraction data showed clear nickel-dependent effects: peak broadening increased with doping, and Scherrer analysis indicated that the coherent crystallite domain size shrank from about 16.2 nanometers in the pristine material to roughly 12.1 nanometers at the highest nickel loading, alongside slight lattice distortion along the c-axis.

Electron microscopy told a complementary story. Field-emission scanning electron microscopy revealed aggregated nanoparticles forming partially porous, interconnected frameworks, with average particle sizes declining steadily from 48.9 nanometers for pristine LSFC to 43.1 nanometers for the Ni0.4 composition. Energy-dispersive X-ray spectroscopy mapping confirmed that lanthanum, strontium, iron, copper, nickel and oxygen were distributed uniformly, with no obvious elemental segregation. High-resolution transmission electron microscopy of the optimized Ni0.4 catalyst resolved lattice fringes with interplanar spacings of 0.268 and 0.277 nanometers, and its selected-area electron diffraction pattern showed concentric polycrystalline rings, consistent with the multiphase structure inferred from X-ray diffraction.

X-ray photoelectron spectroscopy then exposed the surface chemistry that likely underpins the performance gains. The nickel-doped catalyst displayed mixed Ni2+/Ni3+ states in a 62-to-38 ratio, mixed Fe2+/Fe3+ states with Fe2+ dominating at 64.5 percent, and mixed Cu+/Cu2+ contributions. The oxygen 1s spectrum separated lattice metal-oxygen species from higher-binding-energy surface and adsorbed oxygen species. Together, these mixed valences and the altered binding energies of iron and oxygen point to a modified surface electronic environment that can redistribute charge at the electrode-electrolyte interface and facilitate the transfer of electrons to and from oxygen-containing intermediates.

The electrochemical payoff was measured in 0.1 molar potassium hydroxide using a standard three-electrode configuration. For oxygen evolution, the sweet spot was the 40 percent nickel composition, Ni0.4LSFC, which delivered an onset overpotential of just 346 millivolts compared with 440 millivolts for the undoped material, and a Tafel slope of 69.47 millivolts per decade against 138.79 for pristine LSFC. A lower Tafel slope means the current rises much more steeply with each increment of applied voltage, a signature of faster reaction kinetics. The calculated turnover frequency more than tripled, from 4.53 x 10-3 to 14.02 x 10-3 per second, and electrochemical impedance spectroscopy showed the charge-transfer resistance collapsing from 273.7 ohms to 55.24 ohms, the smallest semicircle in the entire series.

For oxygen reduction, a different composition took the lead. Ni0.6LSFC achieved the lowest Tafel slope of the series at 185.68 millivolts per decade, a dramatic improvement over the 396.33 millivolts per decade of pristine LSFC, along with the highest current density of 1.33 milliamperes per square centimeter and the lowest onset potential at 0.570 volts versus reversible hydrogen electrode. The authors candidly place these numbers in context: while nickel incorporation produced a clear and systematic improvement within the LSFC family, the best cobalt-containing and nickel-doped lanthanate catalysts in the literature still post lower ORR Tafel slopes, so the achievement lies in the composition-structure-performance map rather than outright records.

Two additional measurements rounded out the picture. Double-layer capacitance measurements showed that the electrochemically accessible surface area climbed with nickel content, peaking for Ni0.4LSFC, which suggests that smaller particles expose more active sites to the electrolyte. And a five-hour chronoamperometric durability test at 1.7 volts showed the Ni0.4 catalyst holding a nearly constant current with no abrupt loss of activity, with only a 17.6 percent change in current density observed in polarization curves recorded before and after the test. The authors attribute the enhanced bifunctional performance to a synergy of nanostructural refinement, increased electrochemically accessible surface area and nickel-induced electronic modulation through mixed-valence Ni2+/Ni3+ species, while acknowledging that the individual contributions of defects, particle size and the multiphase architecture cannot yet be fully separated.

The broader significance is twofold. Scientifically, the study delivers one of the most systematic correlations to date between progressive B-site nickel substitution and oxygen electrocatalysis in a cobalt-free perovskite, linking phase evolution, crystallite size, surface valence states and charge-transfer kinetics in a single framework. Practically, it strengthens the case that abundant, inexpensive elements such as iron, nickel and copper, arranged in tunable oxide frameworks, can approach the performance territory once reserved for precious metals. If further optimization closes the remaining kinetic gaps, cobalt-free perovskites of this family could become serious contenders for the electrodes of next-generation electrolyzers, fuel cells and metal-air batteries, technologies on which a renewable-powered energy system will increasingly depend.

Subject of Research: Nickel doping of cobalt-free LSFC perovskite oxides for bifunctional oxygen evolution and oxygen reduction electrocatalysis

Article Title: Ni-doped LSFC perovskite oxides for enhanced electrocatalytic performance toward oxygen evolution and oxygen reduction reaction

Article References: Shriwas, P., Behera, S. K., Dewangan, D. K., Singh, M., Thakur, K., Maurya, S. K., Singh, D., Verma, K., Raghuvanshi, A., Uthra, D., Singh, A. K., Azad, U. P., & Singh, A. P. (2026). Ni-doped LSFC perovskite oxides for enhanced electrocatalytic performance toward oxygen evolution and oxygen reduction reaction. Discover Electrochemistry, 3(1), Article 87. https://doi.org/10.1007/s44373-026-00178-3

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00178-3

Keywords: perovskite, electrocatalysis, oxygen evolution reaction, oxygen reduction reaction, nickel doping, LSFC, sol-gel synthesis, X-ray photoelectron spectroscopy, water splitting, fuel cells, Tafel slope, cobalt-free catalysts