Nickel Cobalt Phosphite Nanorods Decorated with Carbon Nanotubes as Bifunctional Electrocatalysts in Alkaline Medium with a High Yield of Hydrogen Peroxide

Abstract

It is highly desirable to develop an energy generation system comprising a low-cost and earth-abundant non-noble metal catalyst for bifunctional electrocatalysis with good overall process performance, especially for applications in fuel cells or metal-air batteries. In this report, we show that nickel cobalt phosphite (NiCoÀ Phi) decorated with carbon nanotubes (CNTs) can perform as a bifunctional electrocatalyst for the oxygen evolution and oxygen reduction reactions (OER and ORR, respectively). The NiCoÀ Phi/CNT composite is synthesized by employing a simple, single-step hydrothermal method. The morphology of the composite consists of nanorod bundles of NiCoÀ Phi decorated with CNTs. The synthesized NiCoÀ Phi/CNT composite exhibits enhanced electrochemical OER activity with an overpotential of 400 mV at a current density of 10 mA/cm 2 and a Tafel slope value of 117 mV dec À 1 in 1 M KOH, possessing high stability towards the OER for 20 h. The ORR using the same catalyst shows an onset potential of 0.75 V and a Tafel slope of 100 mV dec À 1 in 0.1 M KOH with high-yield production of H 2 O 2 (85 %). The predominant formation of H 2 O 2 occurs mainly through a two-electron transfer process, as established by mass-controlled kinetic studies and has not been observed previously in these phosphorous oxy anion-based materials. The superior bifunctional nature of NiCoÀ Phi/CNT towards the OER and ORR arises from the synergistic effect of doped metal phosphites and CNTs.

Role of Metal Ion Sites in Bivalent Cobalt Phosphorus Oxygen Systems toward Efficient Oxygen Evolution Reaction

“…This further supports effective OER for CP-1 than other compounds. The faradaic efficiency of CP-1 has been calculated as 91% using the RRDE 56 (Figure S18). To evaluate and compare the stability of CP-1, CP-2, and CP-3 electrocatalysts at the same current density, we have performed the i−t curve for CP-1 and CP-3 at an applied potential of 1.6 V versus RHE and CP-2 at 1.64 versus RHE.…”

Bacterial cellulose-regulated synthesis of metallic Ni catalysts for high-efficiency electrosynthesis of hydrogen peroxide

“…Furthermore, the high-resolution Ni 2p spectrum (Fig. 2d) shows two primary peaks of Ni 2p 3/2 (855.6 eV) and Ni 2p 1/2 (873.1 eV) with two broad satellite peaks at 861.4 and 879.3 eV, confirming the existence of Ni 2+ [37,38]. Recent reports reported that Ni 2+ centers behave as the active sites for 2e − ORR, thus playing an important role in enhancing the ORR activity and tuning the selectivity [39].…”

Design Strategies of Non‐Noble Metal‐Based Electrocatalysts for Two‐Electron Oxygen Reduction to Hydrogen Peroxide

“…Up to now, various nanostructured transition metal‐based materials such as CoS 2 , [113,114] Mn‐based oxides, [115,116] Fe 3 O 4 , [117] NiCo phosphite, [118] Co 3 O 4 , [119] and Zn‐based MOF [121] have been explored as efficient catalyst towards H 2 O 2 production through the ORR process. Moreover, transition metal compounds are often supported on conductive carbon nanomaterials to improve the conductivity and obtain uniformly dispersed transition metal compounds, thus improving the electrocatalytic performance.…”

“…The P−H group can promote interaction with H 2 O molecules, whereas the O−H group may endow stability in alkaline solution. Nickel cobalt phosphite nanorods/CNTs were synthesized hydrothermally, [118] and the ORR by the composites occurred mainly through the 2e − transfer process with an onset potential of 0.75 V and Tafel slope of 100 mV dec −1 in 0.1 M KOH with H 2 O 2 yield of 85 %. However, the mechanism of 2e − ORR process on doped‐transition metal phosphites is still unexplored.…”