Modulating Hydrogen Exchange Capabilities by Heterogenizing Pd Nanoclusters onto Ni ₃ C Multipods for Efficiently Driving the “Formaldehyde-Nitrate” Tandem Electrochemical System

Abstract

Nitrate and formaldehyde, common industrial byproducts and waterborne pollutants, pose serious environmental and health hazards, yet their efficient conversion remains challenging due to sluggish hydrogen (H*) transfer and limited recycling strategies. While recent studies have explored nitrate reduction (NO 3 RR) and formaldehyde oxidation (FOR) coupling, they faced critical limitations such as no H 2 generation, a lack of electricity output, and reliance on Cu-based catalysts prone to deactivation. This work presents Pd nanoclusters on nickel carbide (Pd nc -Ni 3 C) that serve as a noncopper bifunctional catalyst that possesses superior H* exchange capabilities enabling dual-directional catalysis of NO 3 RR and FOR. At the cathode, Pd nc -Ni 3 C achieves an onset potential of +0.27 V vs RHE, and 98% Faradaic efficiency for NH 3 at −0.3 V. At the anode, Pd nc -Ni 3 C achieves an efficient FOR at a low onset potential of 0.04 V and enables a broad oxidation window (0–1.2 V) with high current density (up to 910 mA cm –2 ), outperforming previously reported Cu- and Ni-based systems. Differential electrochemical mass spectra reveal a previously unexplored intermolecular coupling pathway for H 2 evolution, advancing mechanistic insight into the 1-electron formaldehyde oxidation process. By coupling the NO 3 RR and FOR, a high-performance “Formaldehyde–Nitrate” galvanic cell is achieved with an OCV of 0.88 V and peak power density of 7.4 mW cm –2 . Distinctively, this Ni based system simultaneously converts industrial waste into green energy carriers (H 2, NH 3 ) and value-added chemicals (formate) while producing electricity, offering both environmental and economic benefits.