High‐Performance Bifunctional Electrocatalysts of Palladium Decoration on Carbon Nanoarchitectures for Indirect Releasing of H₂ Stored in Formate

Abstract

Formate has received tremendous research interest as one of the promising organic H2 carriers to store and transport H2 safely and economically. One paramount challenge for implementing the practical feasibility of formate as H2 carrier is how to release H2 at standard pressure and room temperature on demand. Herein, a proof‐of‐concept electrochemical strategy to indirectly release H2 stored in formate in a controlled manner is proposed, in which formate is electrocatalytically oxidized at the alkaline anode to release electrons, which is used for H2 generation at the acidic cathode. For this purpose, highly active bifunctional electrocatalysts with uniformly dispersed Pd nanoparticles supported on a conductive hollow dodecahedron N‐doped carbon network (Pd/hd‐NC), which not only shows one order of magnitude higher catalytic current density than the commercial Pd/C for alkaline formate oxidation reaction (FOR) but is comparable with the commercial Pt/C for acidic hydrogen evolution reaction (HER), are developed. A hybrid alkali/acid cell is developed using Pd/hd‐NC as anode and cathode catalysts of FOR and HER, respectively; in this way, H2 stored in formate can be indirectly released in a tunable manner, which presents significant steps forward, increasing the resiliency of formate as H2 carrier.

Electrochemical Hydrogen Generation by Oxygen Evolution Reaction‐Alternative Anodic Oxidation Reactions

“…Liu et al reported highly active bifunctional electrocatalysts with uniformly dispersed Pd nanoparticles supported on a conductive hollow dodecahedron N‐doped carbon network (Pd/hd‐NC). [ 20 ] A hybrid alkali–acid cell could release H 2 under ambient conditions in a tunable way by adjusting the current or the voltage of the cell. It was capable of discharging voltage of 0.7 and 0.5 V for producing H 2 at a rate of 2.1 and 8.4 mL h −1 , respectively.…”

“…[17] Electrochemical water splitting is considered as the most auspicious strategy for high-purity H 2 generation with thermodynamic voltage of 1.23 V. [18] However, the electrocatalytic reaction consists of multiple elementary reaction steps. [19] The water-splitting process suffers the sluggish anodic oxygen evolution reaction (OER) that imposes high overpotential [20,21] and consumes %90% electrical energy with little economical value of O 2 . [22] Meanwhile, water splitting has the potential issue of the formation of explosive H 2 /O 2 mixture gas during H 2 production.…”

In Situ Construction of Bifunctional N-Doped Carbon-Anchored Co Nanoparticles for OER and ORR

“…Transition-metal (such as Fe, Co, and Ni)-embedded and/ or heteroatom (including N, P, S, B, etc. )-doped 9,10 nanocarbon frameworks have attracted enormous attention as a result of their cost advantage, high chemical stability, comparable electrocatalytic activity to those of precious metals, and adjustable electron distribution property. 11−15 Among them, Co-loaded nitrogen-doped carbon (Co@N−C) materials exhibit satisfactory OER and ORR catalytic performances in alkaline conditions, attributing to the exposed abundant active sites by Co and N species, the high conductivity of C to readily transport electrons, as well as the confinement effect of carbon supports to effectively prevent the growth and aggregation of Co NPs.…”

“…11−15 Among them, Co-loaded nitrogen-doped carbon (Co@N−C) materials exhibit satisfactory OER and ORR catalytic performances in alkaline conditions, attributing to the exposed abundant active sites by Co and N species, the high conductivity of C to readily transport electrons, as well as the confinement effect of carbon supports to effectively prevent the growth and aggregation of Co NPs. 4,10 Meanwhile, the modification of the electron distribution in the C-atomic orbital can optimize the surface adsorption−desorption abilities toward O 2 and OOH* intermediates, which are important factors in boosting the OER and ORR properties in alkaline media. 16−19 Nevertheless, some Co−N−C catalysts, such as self-supported N,Co codoped carbon nanotubes (N,Co-CNTs) 20 and ZIF-8derived Co nanoislands rooted on Co−N−C nanosheets, 21 usually suffer from complex synthesis processes with low yields.…”

“…Transition-metal (such as Fe, Co, and Ni)-embedded and/or heteroatom (including N, P, S, B, etc. )-doped , nanocarbon frameworks have attracted enormous attention as a result of their cost advantage, high chemical stability, comparable electrocatalytic activity to those of precious metals, and adjustable electron distribution property. − Among them, Co-loaded nitrogen-doped carbon (Co@N–C) materials exhibit satisfactory OER and ORR catalytic performances in alkaline conditions, attributing to the exposed abundant active sites by Co and N species, the high conductivity of C to readily transport electrons, as well as the confinement effect of carbon supports to effectively prevent the growth and aggregation of Co NPs. , Meanwhile, the modification of the electron distribution in the C-atomic orbital can optimize the surface adsorption–desorption abilities toward O 2 and OOH* intermediates, which are important factors in boosting the OER and ORR properties in alkaline media. − Nevertheless, some Co–N–C catalysts, such as self-supported N,Co codoped carbon nanotubes (N,Co-CNTs) and ZIF-8-derived Co nanoislands rooted on Co–N–C nanosheets, usually suffer from complex synthesis processes with low yields. Interestingly, metal phthalocyanine can serve as a suitable precursor for the construction of heteroatom-doped nanocarbon frameworks, owning to its intrinsic structure of the center metal atom coordinating with four nitrogen ligands. , However, the high catalytic activity of metal coordination macrocyclic compounds is not well presented due to their commonly poor electrical conductivity.…”