Stable and boosted oxygen evolution efficiency of mixed metal oxide and borate planner heterostructure over heteroatom (N) doped electrochemically exfoliated graphite foam

Ultrathin, large area β-Ni(OH)2 crystalline nanosheet as bifunctional electrode material for charge storage and oxygen evolution reaction

Bifunctional electrode materials are highly desirable for meeting increasing global energy demands and mitigating environmental impact. However, improving the atom-efficiency, scalability, and cost-effectiveness of storage systems, as well as optimizing conversion processes to enhance overall energy utilization and sustainability, remains a significant challenge for their application. Herein, we devised an optimized, facile, economic, and scalable synthesis of large area (cm2), ultrathin (∼2.9 ± 0.3 nm) electroactive nanosheet of β-Ni(OH)2, which acted as bifunctional electrode material for charge storage and oxygen evolution reaction (OER). The β-Ni(OH)2 nanosheet electrode shows the volumetric capacity of 2.82 Ah.cm-3(0.82 µAh.cm-2) at the current density of 0.2 mA.cm-2. The device shows a high capacity of 820 mAh.cm-3 with an ultrahigh volumetric energy density of 0.33 Wh.cm-3 at 275.86 W.cm-3 along with promising stability (30,000 cycles). Furthermore, the OER activity of ultrathin β-Ni(OH)2 exhibits an overpotential (η10) of 308 mV and a Tafel value of 42 mV dec-1 suggesting fast reaction kinetics. The mechanistic studies are enlightened through density functional theory (DFT), which reveals that additional electronic states near the Fermi level enhance activity for both capacitance and OER.

Fabrication of manganese borate/iron carbide encapsulated in nitrogen and boron co-doped carbon nanowires as the accelerated alkaline full water splitting bi-functional electrocatalysts

With high prices of precious metals (such as platinum, iridium, and ruthenium) and transition metals (such as cobalt and nickel), the design of high-efficiency and low-cost non-precious-metal-based catalysts using iron (Fe) and manganese (Mn) metals for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are critical for commercial applications of water splitting devices. In the study, without using any template or surfactant, we successfully designed novel cross-linked manganese borate (Mn3(BO3)2) and iron carbide (Fe3C) embedded into boron (B) and nitrogen (N) co-doped three-dimensional (3D) hierarchically meso/macroporous carbon nanowires (denoted as FexMny@BN-PCFs). Electrochemical test results showed that the HER and OER catalytic activities of Fe1Mn1@BN-PCFs were close to those of 20 wt% Pt/C and RuO2. For full water splitting, (-) Fe1Mn1@BN-PCFs||Fe1Mn1@BN-PCF (+) cell achieved a current density of 10 mA cm-2 at a cell voltage of 1.622 V, which was 14.2 mV larger than that of (-) 20 wt% Pt/C||RuO2 (+) benchmark. The synergistic effect of 3D hierarchically meso/macroporous architectures, excellent charge transport capacity, and abundant active centers (cross-linked Mn3(BO3)2/Fe3C@BNC, BC3, pyridinic-N, MNC, and graphitic-N) enhanced the water splitting catalytic activity of Fe1Mn1@BN-PCFs. The (-) Fe1Mn1@BN-PCFs||Fe1Mn1@BN-PCF (+) cell exhibited excellent stability owing to the superior structural and chemical stabilities of 3D hierarchically porous Fe1Mn1@BN-PCFs.