Strategy for Efficient H₂ Production from a Mixture of Formic Acid and Formate using Operando pH Measurements

Abstract

Formic acid (FA) is a promising hydrogen carrier because it contains 4.3 wt % H2 (53 g H2/L) and releases hydrogen under mild conditions (<80 °C). Previous studies revealed that the coexistence of formate during FA dehydrogenation increases the evolved gas quantity and reaction rate. Most of these studies considered formate a promoter, notwithstanding that formate is a source of H2 and can be dehydrogenated by reacting with water molecules under Pd nanoparticle catalysis. Moreover, formate is considered an intermediate species during FA dehydrogenation. Although the reaction pathways of the dehydrogenation of admixtures of FA and formate are diverse, the determinants thereof remain elusive. We demonstrate that the system proton concentration determines the hydrogen generation pathway. The system pH and composition of the accumulated gas were measured under operando conditions. We introduce the “threshold” point, defined by the specific pH values at which the dehydrogenation pathway utilizes formate instead of FA. The quantity and composition of the produced gas can be actively controlled by tuning the reaction system pH using the threshold point as a standard. Operando monitoring of the pH can help discern whether the gas evolution from the mixture originates from chemical equilibrium or catalyst deactivation.

Efficient Dehydrogenation of Formic Acid at Room Temperature Using a Pd/Chitosan-Derived Nitrogen-Doped Carbon Catalyst: Synthesis, Characterization, and Kinetic Study

“…The sodium formate dehydrogenation route will acquire H protons from H 2 O to complete the hydrogen production process. 32,33 However, the rates of dehydrogenation reactions in pure FA or pure SF solutions were much lower than those in mixed FA/SF solutions (Figure S4), which was attributed to the positive facilitation of FA dehydrogenation reactions by HCOOprovided from sodium formate. The composition of the collected gases was analyzed using GC-TCD (Figure 6b).…”

“…Similar phenomena have been observed in other studies due to the presence of a sodium formate dehydrogenation route in the FA/SF system. The sodium formate dehydrogenation route will acquire H protons from H 2 O to complete the hydrogen production process. , However, the rates of dehydrogenation reactions in pure FA or pure SF solutions were much lower than those in mixed FA/SF solutions (Figure S4), which was attributed to the positive facilitation of FA dehydrogenation reactions by HCOO- provided from sodium formate.…”

Earth-Abundant-Based Photocatalysts for Efficient and Selective H2 Production through Reforming of Formic Acid under Visible Light

“…To date, much effort has been undertaken to produce hydrogen via thermally driven processes in which decomposition of a given hydrogen source, such as liquid organic hydrogen carrier (LOHC), is catalyzed by supported metal species . From among various LOHC, particular attention has been paid to the production of hydrogen from formic acid (FAc) because of its low toxicity, nonflammability, availability, high stability, and high H 2 volumetric capacity (53 kg·m –3 ). − Typically, catalytic decomposition of FAc proceeds via two ways: (1) dehydrogenation (HCOOH → H 2 + CO 2 ) and (2) dehydration (HCOOH → CO + H 2 O) . So far, it has been documented that the former reaction can be conducted efficiently with high selectivity over various supported noble metals. − However, acceptable conversion of FAc into H 2 was usually observed mainly at relatively high temperatures .…”

Fast and Durable Dehydrogenation of Formic Acid over Pd–Cr(OH)3 Nanoclusters Immobilized on Amino-Modified Reduced Graphene Oxide

“…Hydrogen (H 2 ) is a new clean and renewable energy carrier that can replace fossil fuels. , The development of low-cost H 2 production technologies as well as safe and reliable H 2 storage and transportation methods are two major issues that need to be addressed to achieve the large-scale practical application of H 2 energy. , Formic acid (FA, HCOOH) is a renewable, safe, and promising liquid organic hydrogen carrier (LOHC) with low toxicity, low flammability, and high volumetric capacity (53 g of H 2 /L), which can be obtained by biomass processing or CO 2 hydrogenation with green H 2 . − FA can be decomposed via dehydrogenation (HCOOH → H 2 + CO 2 ) and/or dehydration (HCOOH → H 2 O + CO) pathways. − CO produced in the dehydration pathway can poison and deactivate the catalyst in fuel cells, making it necessary to suppress the CO yield to improve the selectivity of the reaction. − …”