Recent Advanced Materials for Electrochemical and Photoelectrochemical Synthesis of Ammonia from Dinitrogen: One Step Closer to a Sustainable Energy Future

Abstract

Ammonia (NH3), an important raw material for chemical industry and agriculture, is also considered to be an intriguing energy storage and transportation media for chemical conversion schemes. The world's primary NH3 supply is based on the natural nitrogen fixation by diazotrophs through an enzymatic nitrogenase process and the industrial nitrogen fixation through a traditional Haber–Bosch process. The natural synthesis of NH3 can hardly meet the rapidly growing global demand. Meanwhile, the industrial NH3 production is still dominated by the high‐temperature and high‐pressure reaction between nitrogen and hydrogen (N2 + 3H2 → 2NH3), requiring intensive energy input and generating massive CO2. Therefore, seeking a breakthrough in the development of catalysts toward efficient ammonia synthesis has become the frontier of energy and chemical conversion schemes. This review summarizes and discusses the recent progress on developing new strategies to optimize the efficiency of NH3 production coupled with renewable energy sources, with a specific focus on electrocatalytic and photoelectrocatalytic conversion of N2 to NH3. The most recent advances in the development of catalytic materials, the design of the reaction systems, and the computational insights for electrochemical and photoelectrochemical ammonia synthesis are covered.

Fundamentals and Recent Progress of Photocatalytic Nitrogen‐Fixation Reaction over Semiconductors

“…[ 54,72–74 ] Also, the electrolytes in the two separate chambers can be different, and thus proper combination of electrolytes can accelerate the photoelectrochemical or photoelectrocatalytic nitrogen‐fixation efficiency. [ 49 ]…”

“…[ 38 ] Subsequently, ultrafine particles of Fe(O)OH and montmorillonite clays loaded with hydrous ferric oxide were also found by the same group to have similar phenomena in the nitrogen‐fixation processes. [ 49 ] They claimed the NO 3 − is from the oxidation of NH 3 , and it was one of the reasons why NH 3 concentrations would reach saturation with the extension of light time. Obviously, there are still great differences and disputes on the mechanism of photocatalytic NOR to form NO and NO 3 − .…”

“…Also, many strategies including manufacturing defects, supporting cocatalysts, and constructing heterojunctions have been developed to improve the nitrogen‐fixation performance. [ 46–49 ]…”

Single‐Atom and Dual‐Atom Electrocatalysts Derived from Metal Organic Frameworks: Current Progress and Perspectives

“…In addition, the Faradic Efficiency for NRR is seriously restricted by the competitive HER owing to the overlapped potential for NRR and HER and the faster HER kinetics. [114] Therefore, designing proper electrocatalysts that can weaken N � N triple bond and suppress HER is very important.…”

Exploration and Investigation of Periodic Elements for Electrocatalytic Nitrogen Reduction

“…Recently, electrocatalytic nitrogen reduction reaction (NRR) has attracted tremendous amount of interest due to its ecofriendly nature (no CO 2 release), ambient reaction conditions, high abundant aqueous electrolytes, and low-cost catalysts. [6][7][8][9][10][11] NRR is a process where N 2 is reformed into NH 3 with the help of suitable catalyst on feeding electricity (N 2 → 2NH 3 + 6H + +6e − ). However, NRR is plagued with low faradaic efficiency.…”