Revealing Ammonia Quantification Minefield in Photo/Electrocatalysis

Abstract

Photo/electrocatalytic ammonia synthesis has recently developed fast while the ammonia yields over state‐of‐the‐art photo/electrocatalysts are still very moderate. Such low concentration of synthesized NH3 brings about a challenge to the reliable quantification of the product in photo/electrocatalysis. Notably, we found that the quantitative detection of ammonia concentration below 0.2 ppm is error‐prone, which is likely the case happening in the majority of photo/electrocatalytic NH3 synthesis, thus arising concerns about the rationality and accuracy for low‐concentration ammonia quantification in these processes. Herein, we discuss the methodology used and analyze the reliability of various detection methods for the detection of trace ammonia in aqueous media. The challenges facing the detection of low concentration of ammonia in photo/electrocatalysis can be overcome by integration with multiple detection methods. According to the data presented, we also propose an effective criterion for precise quantification of ammonia, avoiding the unreasonable comparisons in photo/electrocatalytic ammonia synthesis.

A Reliable and Precise Protocol for Urea Quantification in Photo/Electrocatalysis

“…The urease method mainly refers to the hydrolysis of urea by urease to ammonia, and urea concentration is indirectly calculated by analyzing the net amount of ammonia. Based on our previous ammonia detection studies, [53,54] ion chromatography was adopted to carry out the subsequent ammonia quantitation and the corresponding data are shown in Figure 2a,b and Figures S1 and S2, Supporting Information. Obviously, the peaks at ≈5.5 and ≈8.2 min corresponding to the Na + and K + ions could be observed, and the target ammonia presented its peak at the retention time of ≈6.4 min with an enhanced solution conductance as the urea concentration increased.…”

“…For the urease method, the processes of urease hydrolysis and ammonia detection are susceptible to being disturbed. Based on the detailed studies in ammonia detection that have been explored in photo/electrocatalysis, [53][54][55][56][57][58][59][60][61][62][63][64] the potential interferences in the urease hydrolysis process were summed up including the enzyme concentration, activity, hydrolysis time, temperature, and solution environment. The corresponding interferences were further assessed according to the conservation principle of nitrogen atoms (n [urea] = 2 × n [ammonia] , Figure 3a) and fit degree (R 2 ).…”

Cobalt–Copper Nanoparticles on Three-Dimensional Substrate for Efficient Ammonia Synthesis via Electrocatalytic Nitrate Reduction

“…The amounts of produced ammonia (NH 3 ) in the solution was quantified by using the modified indophenol blue method, ,, which is one of the improved and faster characterization techniques for ammonia detection . In brief, a 1 M NaOH solution containing 5 wt % salicylic acid + 5 wt % sodium citrate (denoted as solution A), 0.05 M NaClO (denoted as solution B), and 1.0 wt % C 5 FeN 6 Na 2 O (denoted as solution C) was prepared in advance.…”

A critical review on layered double hydroxide (LDH)-derived functional nanomaterials as potential and sustainable photocatalysts

“…The primary hurdles lie in the activation of N 2 molecules and kinetic challenges. [80][81][82] The chemisorption of N 2 molecules on top of the active catalytic centers and their subsequent activation by accepting an electron from the catalysts has been facilitated using transition metals (such as Ti, Mo, and Fe) photocatalysts via the formation of N-metal bonds. The vacant d orbitals in the transition metals receives the lone-pair of electrons of N 2 , and the separated electrons in the transition metal atoms are donated to the antibonding orbital (p backdonation), forming an "acceptance-donation" route for the electron transfer that weakens the N^N bond.…”