Particularly, our previous work found that electronegative phosphorus (P) was able to regulate the binding strength of intermediates in ORR and improve the four-electron ORR activity for cobalt phosphide 16. Apart from the metal alloying strategy, incorporation of non-metal elements such as phosphorus, sulfur, and boron into metals to form multicomponent alloys has been demonstrated to be an attractive and effective way to improve the electrocatalytic activity of metal catalysts 11, 12, 13, 14, 15. Elemental leaching hinders the long-term ORR stability and the leached ingredient (particularly toxic Hg) devalues the H 2O 2 product and increases the separation cost 9, 10. However, stability of the bimetallic alloys is a concern, particularly for medicinal or water treatment applications. An ideal two-electron ORR electrocatalyst should possess a suitable binding strength for OOH* (not too strong or too weak) and suppress the O–O bond breakage in OOH* to O*. The goal of secondary metal incorporation is to change the electronic structure of the primary catalytic site and optimize the binding strength of reaction intermediates 8. Bimetallic noble metal alloys, such as Au–Pd, Pt–Hg, Pd–Hg, and Au–Pt–Ni, catalyze ORR through two-electron pathways with selectivity as high as 95% 5, 6, 7. Carbon-based electrocatalysts typically perform well in alkaline solution but show low intrinsic activity and stability in acidic media 4. Many potential ORR electrocatalysts, mainly including carbon-based materials and noble metal-based materials, have been reported for H 2O 2 production in alkaline or acidic electrolyte 3. Incorporation of an efficient and stable catalyst into a proton-exchange membrane electrolyzer or fuel cell is a promising route to commercialization.
However, it is still a great challenge to develop efficient and stable electrocatalysts that are selective toward the two-electron ORR. Electrochemical H 2O 2 production through the oxygen reduction reaction (ORR) in an electrolyzer or fuel cell is an attractive and cost-effective route due to its mild operation conditions, on-site production, and tunable concentration 2. Direct synthesis via H 2 and O 2 is more straightforward but potentially explosive. Furthermore, energy-intensive distillation for obtaining high concentration H 2O 2 is necessary to minimize transportation and storage costs. The anthraquinone process involves multiple redox reaction steps and requires expensive palladium-based hydrogenation catalysts. H 2O 2 is currently manufactured by a large-scale indirect anthraquinone process and the under-developed direct synthesis from a H 2 and O 2 mixture 1.
Hydrogen peroxide (H 2O 2) is a valuable chemical for a variety of industrial applications, as well as a potential energy carrier alternative to oil or hydrogen in fuel cells. Catalyst stability enables an accumulated neutral H 2O 2 concentration in 600 mL of 3.0 wt% (pH = 6.6). Atomic layer deposition of Al 2O 3 prevents NC aggregation and enables application in a polymer electrolyte membrane fuel cell (PEMFC) with a maximum r(H 2O 2) of 2.26 mmol h −1 cm −2 and a current efficiency of 78.8% even at a high current density of 150 mA cm −2. Density functional theory calculations indicate that P promotes hydrogenation of OOH* to H 2O 2 by weakening the Pt-OOH* bond and suppressing the dissociative OOH* to O* pathway.
We report ultrasmall and monodisperse colloidal PtP 2 nanocrystals that achieve H 2O 2 production at near zero-overpotential with near unity H 2O 2 selectivity at 0.27 V vs. Despite progress in small scale electrocatalytic production of hydrogen peroxide (H 2O 2) using a rotating ring-disk electrode, further work is needed to develop a non-toxic, selective, and stable O 2-to-H 2O 2 electrocatalyst for realizing continuous on-site production of neutral hydrogen peroxide.