A hybrid heteronanostructure of α-MnO 2 /Mn 3 O 4 /CeO 2 with the atomic-level coupled nanointerface entrenched in Vulcan carbon is reported and explored for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). CeO 2 plays an essential role in increasing the surface Mn 2+/3+/4+ in α-MnO 2 /Mn 3 O 4 /CeO 2 /C for ORR/OER processes. It shows enhanced bifunctional activity, superior to that of the benchmark 20 wt % Pt/C and Pd/C catalysts. It displays an ORR onset potential of −0.13 V (vs Ag/AgCl), limiting current density of −6.63 mA cm −2 (at 1600 rpm), mass-specific current of 47.6 mA mg MO −1 with a lower Tafel slope (921.9 mV dec −1 ), and an inclusive 4-e transfer involved in ORR. The OER onset potential and current density are 0.58 V (vs Ag/AgCl) and 8.45 mA cm −2 (at 0.8 V). The unique hybrid structure with oxide−oxide interface in α-MnO 2 / Mn 3 O 4 /CeO 2 is correlated to explain the mechanistic pathway. Multistate Mn(II/III/IV) and Ce(III/IV) synergistically influence in tendering superior activity with enhanced stability.

Oxygen reduction reaction (ORR) is one of the fundamental reactions that occur on the cathode of fuel cells. The sluggish kinetics of ORR and the high cost of the conventionally used ORR electrocatalyst mandate extensive research towards the development of inexpensive, high-performance and stable electrocatalysts. Various supported nanostructures of pristine noble metals and its alloys, transition metals/metal oxides (MOs), chalcogens/pnictogens doped metals/MOs, etc. have attracted great attention towards ORR in both acidic and alkaline electrolytes. This review primarily documents the recent advancements and challenges of supported nanomaterials with fascinating properties towards ORR. This study focuses on the use of carbon-based materials as support. The significant factors like size, morphology, hetero-atom doping, defects and interfaces (metal/metal, metal/oxide and metal/hydroxide) that can tailor ORR activity are portrayed elaborately. The electrochemical techniques and parameters that are adopted mainly during data collection and evaluation of ORR are also discussed.

This work reports a simple chemical route to synthesize high surface area ceria (CeO2) nanoparticles which exhibit remarkable radical scavenging activity. Synthesized CeO2 nanoparticles are characterized by thermogravimetric analysis (TGA), X‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FTIR) and Raman spectroscopy, scanning electron microscopy (SEM), energy‐dispersive X‐ray analysis (EDX), transmission electron microscopy (TEM), and Brunauer‐Emmett‐Teller surface area (BET surface area) analyses. The characterization results reveal the formation of cubic phase of CeO2 with particles sizes of 10 nm and a remarkably high specific surface area of 236.8 m2/g. The nanoparticles are explored for 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) and hydroxyl radical scavenging activity that is to assess the antioxidant property of nanoceria by in‐vitro spectrophotometric approach.

We report a controllable synthesis of Co 3 O 4 nanooctahedron anchored on Vulcan XC 72R (Oct-Co 3 O 4 /C) to explore the crystal symmetry effects on the bifunctional electrocatalysis of oxygen reduction and oxygen evolution reaction (ORR/OER) in alkaline electrolyte. Systematic electrochemical measurements reveal that Oct-Co 3 O 4 /C exhibits remarkable ORR/OER activity with a higher ORR onset potential (E onset = 0.89 V), half-wave potential (E 1/2 = 0.68 V), large limiting current density (j = −6.38 mA cm −2 ), and significantly lower overpotential for 10% energy conversion (η 10 = 0.45 V). The superior bifunctional activity can be attributed to the synergistic contribution of high specific surface area (131.3 m 2 g −1 ), electrochemically active surface area (ECSA = 35.83 m 2 g −1 ), and rich oxygen vacancies in the well-defined octahedral crystal symmetry. Furthermore, the chronoamperometric and accelerated durability test demonstrated superior stability and durability for the catalytic process. This study underscores the significance of morphology control in the design of an advanced ORR/OER electrocatalyst in alkaline medium.

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Herein, we report a systematic study of nanohybrids (NHs) of various FeÀ Co oxides anchored on to carbon matrix for highperforming oxygen electrode reactions. Fe 2.1 Co 0.9 O 4 /C NH having minor content of Co 3 + exhibited superior oxygen reduction reaction (ORR) performance than the other compositions and benchmark Pt/C. It exhibits a current density of 8.4 mA cm À 2 in 0.1 M KOH for ORR compared to the benchmark Pt/C (3.81 mA cm À 2 ). It also reveals superior stability and durability than Pt/C. It can retain 92 % of its initial current up to 7000 s. Also, the Fe 2.1 Co 0.9 O 4 /C NH delivers the best Tafel slope of 72.6 mV dec À 1 . Additionally, the Co 3 + rich Fe 0.9 Co 2.1 O 4 /C NH demonstrated superior oxygen evolution reaction (OER) performance than the Pt/C, RuO 2 and other compositions in 0.1 M KOH solution. Thus, the obtained electrocatalysts (ECs) having bimetallic active site demonstrates unique electrocatalytic properties and the carbon matrix can increase stability and thus provide additional catalytic active sites. This makes them a significant candidate for oxygen electrocatalysis.

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Pd-based electrocatalysts are considered as suitable replacement for Pt-based ones owing to the similar electronic structure of Pd, relatively low cost, and superior catalytic performance. The activity and utilization efficiency of Pd in electrochemical reactions can be increased by alloying with transition metals, like Cu and Co. Herein, we report the synthesis of a homogeneously embedded Pd 2 CuCo alloy in the carbon matrix. Compared with the benchmark Pt/C, the as-synthesized Pd alloy electrocatalyst exhibited an improved limiting current density (J m ; −5.65 mA cm −2 ), a smaller Tafel slope (58.7 mV dec −1 ), and a comparable onset potential (E onset ; 0.91 V vs RHE). Comparatively, the optimized Pd 2 CuCo showed a current retention of ∼96% after a 6 h stability test and only a 4 mV loss in the half-wave potential (E 1/2 ) after 10,000 redox cycles, while Pt/C showed a current retention of 72.5% and a loss of 5 mV in E 1/2 . Meanwhile, the Pd 2 CuCo alloy electrocatalyst also demonstrated excellent methanol tolerance compared to benchmark Pt/C. In addition, the electrocatalyst showed higher activity and long-term stability toward the formic acid oxidation reaction than Pd/C, signifying the potential for wide applicability.