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 Fe_xMn_y@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, M–N–C, 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.