Nanoparticles Na4Ni3Р4О15-Ni(OH)2 Core-Shell as hybrid electrocatalyst for the oxygen evolution reaction in alkaline electrolyte

There are wide interests in developing efficient, robust and low-cost electrode materials for electrolysis of water to produce clean hydrogen fuel. It is especially important to improve the performance and durability of electrocatalysts for OER. Here we showed that the transformation of nanoparticles (n-NNP) and crystalline (c-NNP) forms of mixed phosphate Na4Ni3(PO4)2P2O7 in highly alkaline solutions occurs along various routes and provokes generation of 2D-nanosheets Ni(OH)2 or stable particles of core(phosphate)-shell(Ni(OH)2), respectively. In both cases, in carbon matrix (through chemical and electrochemical conversion of phosphate in situ during electrolysis in 6 M KOH or NaOH solution) stable OER electrocatalysts with low overpotentials of 250-290 mV at a current density of 10 mA·cm-2 were obtained. The best candidate for OER process is core-shell particles, which maintain overpotentials of around 250 mV in 6 M KOH more than 3 days. The activity enhancement can be attributed to formation of abundant system of NiOOH nanoparticles on the shell surface due to improved lattice matching. The report discusses further prospects for the creation of core-shell particles to reduce the overpotential of durable electrocatalysts for OER.