To further investigate the structure of the synthesized catalysts, all four materials were characterized by XRD(Figure ). The major peaks corresponding to the spinel phase are found at 31.3°, 36.9°, 44.8°, 59.4° and 65.2°, which are the characteristic peaks of Co3O4 . The peaks at 44.8° and 55.0° found in all four spectra can be attributed to the carbon paper substrate (Figure ). The presence of the spinel peaks in all four spectra demonstrates that spinel oxides have been successfully synthesized in all four cases. However, in addition to the peaks corresponding to the spinel oxide and the carbon substrate phases, new peaks corresponding to a different phase also appear in the Co-Ga and Co-Al oxide spectra. These can be attributed to β-Ga2O3 in Co-Ga oxide spectra and θ-Al2O3 in the Co-Al oxide spectrum . Since neither Ga2O3 nor Al2O3 are redoxactive, they are unlikely to make any significant contribution to OER activity . The composition of the synthesized materials was characterized with XPS (Figures ). The high-resolution Co2p spectra of each of these materials (Figures ) show evidence of spinorbit splitting into 2p3/2 and 2p1/2 components at ~780eV and ~795 eV respectively, with shake-up satellites for each of these components present at ~790eV and ~805eV . Each of these spectra resembles the Co2p spectra of Co3O4, further corroborating the results of the XRD that have demonstrated the successful synthesis of cobalt spinel oxide . In order to determine the stoichiometry of each of these catalysts, the Co2p 2/3 spectra were deconvoluted based on the Co2p 2/3 peak fitting parameters by Biesinger et al. and the ratio between the areas of the peaks associated with the Co 2+ and Co 3+ oxidation states were calculated . Since both Ga and Al are not stable in the +2 oxidation state, they are both likely to displace Co 3+ if successfully incorporated into the spinel oxide structure. Thus, comparing the Co 2+ and Co 3+ ratio will help determine the stoichiometry. The ratios of the peak areas of Co 2+ to Co 3+ are 1:2, 1:0.7, 1:1.5 and 1:1 in the Co3O4, Co-Al, and the two Co-Ga catalysts respectively. This indicates that the exact structural formulae of the catalysts are Co3O4, Co1.7Al1.3O4, Co2.5Ga0.5O4 and GaCo2O4. Benchmarking catalysts in this study with other state-of-the-art catalysts reported in the literature. Each experiment in our plot was done in 1M KOH solution. A more detailed breakdown of each reference catalyst can be seen in Table After the synthesis and structural characterization of these catalysts, they were electrochemically characterized for OER activity by linear sweep voltammetry (LSV) in a 1M KOH solution (Figure ). The overpotential in this report is defined as the iR-corrected potential at 10mA/cm 2 geo minus 1.23V, where geo represents the geometric surface area. At 10mA/cm 2 geo of current density, Co3O4 has the lowest overpotential of all the catalysts at 170mV, followed by Co1.7Al1.3O4 at 193mV, Co2.5Ga0.5O4 at 220mV and finally GaCo2O4 at 270mV. However, while Co2.5Ga0.5O4 has a higher overpotential than either Co3O4 or Co1.7Al1.3O4, it also has a much lower Tafel slope at 56.0 mV.dec -1 than either catalyst(Figure ). This allows Co2.5Ga0.5O4 to start outcompeting the rest of the catalysts at around 1.55VRHE.