# Bipolar Hydrogen Production from a Hybrid Alkaline‐Acidic Formaldehyde‐Proton Fuel Cell

## TL;DR

A new fuel cell design uses formaldehyde oxidation and hydrogen evolution to produce hydrogen and electricity more efficiently than traditional methods.

## Contribution

A hybrid alkaline-acidic formaldehyde-proton fuel cell is introduced, enabling bipolar hydrogen production with enhanced efficiency and electricity generation.

## Key findings

- The hybrid FPFC achieves a significantly reduced ΔrGmθ of −101.5 kJ mol−1.
- A Ru-doped Cu catalyst enables concurrent H2 production and electricity generation with a peak power density of 18.3 mW cm−2.
- The FPFC achieves a Faradaic efficiency of 400% for H2 production when used to drive water splitting.

## Abstract

Due to a positive standard reaction Gibbs free energy (Δr
G
m
θ) of 237.1 kJ mol−1, electric energy input is indispensable for hydrogen production by conventional electrochemical water splitting. This energy requirement can be reduced by replacing the anodic oxygen evolution reaction to thermodynamic favorable small‐molecules oxidation reactions. In this work, anodic formaldehyde oxidation reaction (FOR) in alkaline media was paired with cathodic hydrogen evolution reaction (HER) in acidic media to establish a thermodynamically downhill system. The utilization of electrochemical neutralization energy in a hybrid alkaline‐acidic electrolyte configuration enables a further decrease in Δr
G
m
θ. Therefore, the resulting hybrid alkaline‐acidic formaldehyde‐proton fuel cell (FPFC) exhibits a significantly reduced Δr
G
m
θ of −101.5 kJ mol−1. A bifunctional Ru‐doped Cu catalyst (Ru─Cu NTs@CM) was designed and synthesized to simultaneously promote the kinetics of acidic HER and alkaline FOR, demonstrating superior catalytic activity and durability to pristine Cu and Ru catalysts. This catalyst enabled concurrent bipolar H2 production and electricity generation from the assembled FPFC, reaching a peak power density of 18.3 mW cm−2 at 53.4 mA cm−2. A combination of (quasi) in situ characterizations and theoretical calculations unveiled the important mechanistic role of Ru‐doping in enhancing the Cu catalyst's activity and stability.

A novel hybrid alkaline‐acidic formaldehyde‐proton fuel cell (FPFC) was developed by coupling alkaline formaldehyde oxidation reaction (FOR) with acidic hydrogen evolution reaction (HER). This design enables concurrent bipolar H2 production and electricity generation. The electricity produced by the FPFC can be used to drive the operation of FOR‐assisted water splitting, achieving a promising Faradaic efficiency of 400% for H2 production.