CO₂‐Mediated H₂ Storage‐Release with Nanostructured Catalysts: Recent Progresses, Challenges, and Perspectives

Abstract

It has increasingly become clear that economic growth worldwide based on fossil fuel energy supply cannot be sustained; thus, alternative, renewable energy sources and carriers must be urgently developed to maintain growth. Dihydrogen (H2), which can produce energy without generating environmental pollutants, can play a major role in this endeavor. However, to use H2 in renewable energy systems, systems and materials that can store and transport it, or convert it into easier‐to‐handle/transport synthetic fuels, need to be developed. In this article, first, many of the issues related to both homogeneous and heterogeneous catalysts that are being developed to help H2's use as energy carrier are discussed. More focus is then given to heterogeneous nanocatalysts that are developed for reversible CO2‐mediated hydrogenation and dehydrogenation reactions involving chemical hydrogen carriers and delivery systems, mainly formic acid/CO2 and formate/bicarbonate. The challenges associated with the development of nanocatalysts based on earth‐abundant elements for dehydrogenation and hydrogenation reactions of these compounds for H2 storage and release are emphasized in the discussions. Finally, the pressing research questions and major issues that need to be addressed in the near future to help the realization of the “hydrogen economy” are outlined.

Chemical Batteries with CO2

“…Ac entral role for chemistry will be the storage and transport of renewable energy,w hich is initially produced as electricity,sothat this energy can become aglobally available traded commodity. [28] This operation will require "green oil and green gas [30] "a nd depend to as ignificant extent on chemical batteries.M ethane,m ethanol, [30] LOHC, [31] and ammonia [32] are currently crucial substances for this purpose. Thet ask of replacing fossil energy carriers will be difficult without the chemical reduction of CO 2 .I ti sf or this reason that the chemically simple,b ut urgently needed products arising from the reduction of CO 2 to "solar fuels" are the most valuable products [33] in the defossilization of the energy industry despite their low specific economic added value when compared to chemically complex molecules from the chemical industry.…”

Heterogeneous catalysts for CO2hydrogenation to formic acid/formate: from nanoscale to single atom

“…Heterogeneous CO 2 reduction to formic acid/formate has been comprehensively summarized in several reviews from different perspectives, 35,44,[63][64][65][66] covering aspects of catalytic materials, reaction parameters, process engineering, and mechanistic insights. In recent years, the rapid development of single atom catalysis has given rise to an increasing number of SACs featuring high activity for CO 2 reduction to formic acid/formate.…”

Visible-Light Acceleration of H2 Evolution from Aqueous Solutions of Inorganic Hydrides Catalyzed by Gold-Transition-Metal Nanoalloys

“…[19][20][21][22][23] Inorganic hydrides such as AB and sodium borohydride, NaBH4, are promising hydrogen storage compounds, [24][25][26] because they are stable solids with high colloidal solubility in water, contain a high proportion of hydrogen and are easily transported contrary to explosive hydrogen gas. 27,28 Also, AB is inert toward hydrolysis, and NaBH4 is hydrolyzed only very slowly in the absence of catalyst. 29 Therefore, research efforts have recently been devoted to the optimization of catalysts for H2 generation from water and such inorganic hydrides.…”